processor/otel: Java exceptions thrown by Spring Reactive are not parsed correctly

**APM Server version** (`apm-server version`): 7.15.2

**Description of the problem including expected versus actual behavior**:

Exceptions thrown in Spring Reactive application code, when captured by OpenTelemetry Java auto instrumentation, are not parsed correctly by the processor/otel.

**Steps to reproduce**:

See https://discuss.elastic.co/t/stack-trace-is-not-parsed/292179

Sample exception:

```
org.springframework.web.reactive.function.client.WebClientRequestException: Connection refused: no further information: localhost/127.0.0.1:8090; nested exception is io.netty.channel.AbstractChannel$AnnotatedConnectException: Connection refused: no further information: localhost/127.0.0.1:8090
at org.springframework.web.reactive.function.client.ExchangeFunctions$DefaultExchangeFunction.lambda$wrapException$9(ExchangeFunctions.java:141)
Suppressed: The stacktrace has been enhanced by Reactor, refer to additional information below:
Error has been observed at the following site(s):
*__checkpoint ⇢ Request to GET null [DefaultWebClient]
Original Stack Trace:
at org.springframework.web.reactive.function.client.ExchangeFunctions$DefaultExchangeFunction.lambda$wrapException$9(ExchangeFunctions.java:141)
at reactor.core.publisher.MonoErrorSupplied.subscribe(MonoErrorSupplied.java:55)
at reactor.core.publisher.Mono.subscribe(Mono.java:4400)
at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onError(FluxOnErrorResume.java:103)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.lambda$onError$2(TracingSubscriber.java:63)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.withActiveSpan(TracingSubscriber.java:79)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.onError(TracingSubscriber.java:63)
at reactor.core.publisher.FluxPeek$PeekSubscriber.onError(FluxPeek.java:222)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.lambda$onError$2(TracingSubscriber.java:63)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.withActiveSpan(TracingSubscriber.java:79)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.onError(TracingSubscriber.java:63)
at reactor.core.publisher.FluxPeek$PeekSubscriber.onError(FluxPeek.java:222)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.lambda$onError$2(TracingSubscriber.java:63)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.withActiveSpan(TracingSubscriber.java:79)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.onError(TracingSubscriber.java:63)
at reactor.core.publisher.FluxPeek$PeekSubscriber.onError(FluxPeek.java:222)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.lambda$onError$2(TracingSubscriber.java:63)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.withActiveSpan(TracingSubscriber.java:79)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.onError(TracingSubscriber.java:63)
at reactor.core.publisher.MonoNext$NextSubscriber.onError(MonoNext.java:93)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.lambda$onError$2(TracingSubscriber.java:63)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.withActiveSpan(TracingSubscriber.java:79)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.onError(TracingSubscriber.java:63)
at reactor.core.publisher.MonoFlatMapMany$FlatMapManyMain.onError(MonoFlatMapMany.java:204)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.lambda$onError$2(TracingSubscriber.java:63)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.withActiveSpan(TracingSubscriber.java:79)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.onError(TracingSubscriber.java:63)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.lambda$onError$2(TracingSubscriber.java:63)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.withActiveSpan(TracingSubscriber.java:79)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.onError(TracingSubscriber.java:63)
at reactor.core.publisher.FluxContextWrite$ContextWriteSubscriber.onError(FluxContextWrite.java:121)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.lambda$onError$2(TracingSubscriber.java:63)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.withActiveSpan(TracingSubscriber.java:79)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.onError(TracingSubscriber.java:63)
at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onError(FluxOnErrorResume.java:106)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.lambda$onError$2(TracingSubscriber.java:63)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.withActiveSpan(TracingSubscriber.java:79)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.onError(TracingSubscriber.java:63)
at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.onError(MonoIgnoreThen.java:270)
at reactor.core.publisher.Operators.error(Operators.java:198)
at reactor.core.publisher.MonoError.subscribe(MonoError.java:53)
at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)
at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.subscribeNext(MonoIgnoreThen.java:236)
at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.onComplete(MonoIgnoreThen.java:203)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.withActiveSpan(TracingSubscriber.java:79)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.onComplete(TracingSubscriber.java:68)
at reactor.core.publisher.FluxPeek$PeekSubscriber.onComplete(FluxPeek.java:260)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.withActiveSpan(TracingSubscriber.java:79)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.onComplete(TracingSubscriber.java:68)
at reactor.core.publisher.Operators$ScalarSubscription.request(Operators.java:2400)
at reactor.core.publisher.FluxPeek$PeekSubscriber.request(FluxPeek.java:138)
at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.onSubscribe(MonoIgnoreThen.java:134)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.lambda$onSubscribe$0(TracingSubscriber.java:53)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.withActiveSpan(TracingSubscriber.java:79)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.onSubscribe(TracingSubscriber.java:53)
at reactor.core.publisher.FluxPeek$PeekSubscriber.onSubscribe(FluxPeek.java:171)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.lambda$onSubscribe$0(TracingSubscriber.java:53)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.withActiveSpan(TracingSubscriber.java:79)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.onSubscribe(TracingSubscriber.java:53)
at reactor.core.publisher.MonoJust.subscribe(MonoJust.java:55)
at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)
at reactor.core.publisher.MonoDeferContextual.subscribe(MonoDeferContextual.java:55)
at reactor.core.publisher.Mono.subscribe(Mono.java:4400)
at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.subscribeNext(MonoIgnoreThen.java:255)
at reactor.core.publisher.MonoIgnoreThen.subscribe(MonoIgnoreThen.java:51)
at reactor.core.publisher.Mono.subscribe(Mono.java:4400)
at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onError(FluxOnErrorResume.java:103)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.lambda$onError$2(TracingSubscriber.java:63)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.withActiveSpan(TracingSubscriber.java:79)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.onError(TracingSubscriber.java:63)
at reactor.core.publisher.SerializedSubscriber.onError(SerializedSubscriber.java:124)
at reactor.core.publisher.FluxRetryWhen$RetryWhenMainSubscriber.whenError(FluxRetryWhen.java:225)
at reactor.core.publisher.FluxRetryWhen$RetryWhenOtherSubscriber.onError(FluxRetryWhen.java:274)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.lambda$onError$2(TracingSubscriber.java:63)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.withActiveSpan(TracingSubscriber.java:79)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.onError(TracingSubscriber.java:63)
at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.innerError(FluxConcatMap.java:309)
at reactor.core.publisher.FluxConcatMap$ConcatMapInner.onError(FluxConcatMap.java:873)
at reactor.core.publisher.Operators.error(Operators.java:198)
at reactor.core.publisher.MonoError.subscribe(MonoError.java:53)
at reactor.core.publisher.Mono.subscribe(Mono.java:4400)
at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.drain(FluxConcatMap.java:449)
at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.onNext(FluxConcatMap.java:251)
at reactor.core.publisher.EmitterProcessor.drain(EmitterProcessor.java:491)
at reactor.core.publisher.EmitterProcessor.tryEmitNext(EmitterProcessor.java:299)
at reactor.core.publisher.SinkManySerialized.tryEmitNext(SinkManySerialized.java:100)
at reactor.core.publisher.InternalManySink.emitNext(InternalManySink.java:27)
at reactor.core.publisher.FluxRetryWhen$RetryWhenMainSubscriber.onError(FluxRetryWhen.java:190)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.lambda$onError$2(TracingSubscriber.java:63)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.withActiveSpan(TracingSubscriber.java:79)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.onError(TracingSubscriber.java:63)
at reactor.core.publisher.MonoCreate$DefaultMonoSink.error(MonoCreate.java:194)
at reactor.netty.http.client.HttpClientConnect$MonoHttpConnect$ClientTransportSubscriber.onError(HttpClientConnect.java:304)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.lambda$onError$2(TracingSubscriber.java:63)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.withActiveSpan(TracingSubscriber.java:79)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.onError(TracingSubscriber.java:63)
at reactor.core.publisher.MonoCreate$DefaultMonoSink.error(MonoCreate.java:194)
at reactor.netty.resources.DefaultPooledConnectionProvider$DisposableAcquire.onError(DefaultPooledConnectionProvider.java:172)
at reactor.netty.internal.shaded.reactor.pool.AbstractPool$Borrower.fail(AbstractPool.java:477)
at reactor.netty.internal.shaded.reactor.pool.SimpleDequePool.lambda$drainLoop$9(SimpleDequePool.java:401)
at reactor.core.publisher.FluxDoOnEach$DoOnEachSubscriber.onError(FluxDoOnEach.java:186)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.lambda$onError$2(TracingSubscriber.java:63)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.withActiveSpan(TracingSubscriber.java:79)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.onError(TracingSubscriber.java:63)
at reactor.core.publisher.MonoCreate$DefaultMonoSink.error(MonoCreate.java:194)
at reactor.netty.resources.DefaultPooledConnectionProvider$PooledConnectionAllocator$PooledConnectionInitializer.onError(DefaultPooledConnectionProvider.java:554)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.lambda$onError$2(TracingSubscriber.java:63)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.withActiveSpan(TracingSubscriber.java:79)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.onError(TracingSubscriber.java:63)
at reactor.core.publisher.MonoFlatMap$FlatMapMain.secondError(MonoFlatMap.java:192)
at reactor.core.publisher.MonoFlatMap$FlatMapInner.onError(MonoFlatMap.java:259)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.lambda$onError$2(TracingSubscriber.java:63)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.withActiveSpan(TracingSubscriber.java:79)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.onError(TracingSubscriber.java:63)
at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onError(FluxOnErrorResume.java:106)
at reactor.core.publisher.Operators.error(Operators.java:198)
at reactor.core.publisher.MonoError.subscribe(MonoError.java:53)
at reactor.core.publisher.Mono.subscribe(Mono.java:4400)
at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onError(FluxOnErrorResume.java:103)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.lambda$onError$2(TracingSubscriber.java:63)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.withActiveSpan(TracingSubscriber.java:79)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.onError(TracingSubscriber.java:63)
at reactor.core.publisher.FluxPeekFuseable$PeekFuseableSubscriber.onError(FluxPeekFuseable.java:234)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.lambda$onError$2(TracingSubscriber.java:63)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.withActiveSpan(TracingSubscriber.java:79)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.onError(TracingSubscriber.java:63)
at reactor.core.publisher.FluxHide$SuppressFuseableSubscriber.onError(FluxHide.java:142)
at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.onError(MonoPeekTerminal.java:258)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.lambda$onError$2(TracingSubscriber.java:63)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.withActiveSpan(TracingSubscriber.java:79)
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.TracingSubscriber.onError(TracingSubscriber.java:63)
at reactor.core.publisher.FluxHide$SuppressFuseableSubscriber.onError(FluxHide.java:142)
at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.onError(MonoPeekTerminal.java:258)
at reactor.netty.transport.TransportConnector$MonoChannelPromise.tryFailure(TransportConnector.java:517)
at reactor.netty.transport.TransportConnector$MonoChannelPromise.setFailure(TransportConnector.java:471)
at reactor.netty.transport.TransportConnector.lambda$doConnect$7(TransportConnector.java:206)
at io.opentelemetry.javaagent.instrumentation.netty.common.FutureListenerWrappers$WrappedFutureListener.operationComplete(FutureListenerWrappers.java:106)
at io.netty.util.concurrent.DefaultPromise.notifyListener0(DefaultPromise.java:578)
at io.netty.util.concurrent.DefaultPromise.notifyListeners0(DefaultPromise.java:571)
at io.netty.util.concurrent.DefaultPromise.notifyListenersNow(DefaultPromise.java:550)
at io.netty.util.concurrent.DefaultPromise.notifyListeners(DefaultPromise.java:491)
at io.netty.util.concurrent.DefaultPromise.setValue0(DefaultPromise.java:616)
at io.netty.util.concurrent.DefaultPromise.setFailure0(DefaultPromise.java:609)
at io.netty.util.concurrent.DefaultPromise.tryFailure(DefaultPromise.java:117)
at io.netty.channel.nio.AbstractNioChannel$AbstractNioUnsafe.fulfillConnectPromise(AbstractNioChannel.java:321)
at io.netty.channel.nio.AbstractNioChannel$AbstractNioUnsafe.finishConnect(AbstractNioChannel.java:337)
at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:707)
at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:655)
at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:581)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:493)
at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:986)
at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
at java.base/java.lang.Thread.run(Thread.java:834)
Suppressed: java.lang.Exception: #block terminated with an error
at reactor.core.publisher.BlockingSingleSubscriber.blockingGet(BlockingSingleSubscriber.java:99)
at reactor.core.publisher.Mono.block(Mono.java:1707)
at ExceptionTest.testSpan(ExceptionTest.java:22)
at ExceptionTest.main(ExceptionTest.java:13)
Caused by: io.netty.channel.AbstractChannel$AnnotatedConnectException: Connection refused: no further information: localhost/127.0.0.1:8090
Caused by: java.net.ConnectException: Connection refused: no further information
at java.base/sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
at java.base/sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:779)
at io.netty.channel.socket.nio.NioSocketChannel.doFinishConnect(NioSocketChannel.java:330)
at io.netty.channel.nio.AbstractNioChannel$AbstractNioUnsafe.finishConnect(AbstractNioChannel.java:334)
at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:707)
at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:655)
at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:581)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:493)
at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:986)
at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
at java.base/java.lang.Thread.run(Thread.java:834)
```