Improve exit code reporting to detect runtime crashes

Currently, when app crashes and there is no exit code set, XHarness will report `TCP_CONNECTION_FAILED`.
https://github.com/dotnet/xharness/blob/35965f58a6c3b98aac88b2859eaac36dc6395d1a/src/Microsoft.DotNet.XHarness.Apple/Orchestration/TestOrchestrator.cs#L325-L330

If possible, we should distinguish between failures in establishing TCP connection (device not ready/offline) and sudden lost of connection (likely runtime crash).

E.g. https://dev.azure.com/dnceng-public/public/_build/results?buildId=764645&view=ms.vss-test-web.build-test-results-tab&runId=19449412&resultId=100007&paneView=dotnet-dnceng.dnceng-build-release-tasks.helix-test-information-tab reports
`XHarness exit code: 92 (TCP_CONNECTION_FAILED)` while `net.dot.System.Runtime.Tests.log` shows SEGFAULT at `System.Threading.LazyInitializer:EnsureLockInitialized`.