fat jars incorrectly shade kotlin-reflect

The shaded kotlin reflect API tries to load a resource at the wrong path, causing:

```
java.lang.IllegalStateException: Resource not found in classpath: kotlin/kotlin.kotlin_builtins
at org.pkl.thirdparty.kotlin.reflect.jvm.internal.impl.serialization.deserialization.builtins.BuiltInsLoaderImpl.createBuiltInPackageFragmentProvider(BuiltInsLoaderImpl.kt:59)
at org.pkl.thirdparty.kotlin.reflect.jvm.internal.impl.serialization.deserialization.builtins.BuiltInsLoaderImpl.createPackageFragmentProvider(BuiltInsLoaderImpl.kt:35)
at org.pkl.thirdparty.kotlin.reflect.jvm.internal.impl.builtins.KotlinBuiltIns.createBuiltInsModule(KotlinBuiltIns.java:105)
at org.pkl.thirdparty.kotlin.reflect.jvm.internal.impl.builtins.DefaultBuiltIns.(DefaultBuiltIns.kt:24)
at org.pkl.thirdparty.kotlin.reflect.jvm.internal.impl.builtins.DefaultBuiltIns.(DefaultBuiltIns.kt:21)
at org.pkl.thirdparty.kotlin.reflect.jvm.internal.impl.builtins.DefaultBuiltIns.(DefaultBuiltIns.kt:31)
```

Start by reproducing the failure when using a fat jar, then inspect how kotlin-reflect is shaded and how its built-in resource is packaged. Done means the shaded artifact can load kotlin/kotlin.kotlin_builtins without raising the reported IllegalStateException.

Written by the indexing model from the issue text.