Improve uncaught exception handling ("Internal Error" popups)

[fwcd]

Currently uncaught exceptions on the server side result in a generic "Internal Error" popup in VSCode:

The reason for this is that LSP4J places the stacktrace in the data field which is apparently ignored on the client side:

Content-Length: 2789

{
    "jsonrpc": "2.0",
    "id": 0,
    "error": {
        "code": -32603,
        "message": "Internal error.",
        "data": "java.lang.RuntimeException: java.lang.reflect.InvocationTargetException\r\n\tat org.eclipse.lsp4j.jsonrpc.services.GenericEndpoint.lambda$null$0(GenericEndpoint.java:67)\r\n\tat org.eclipse.lsp4j.jsonrpc.services.GenericEndpoint.request(GenericEndpoint.java:120)\r\n\tat org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.handleRequest(RemoteEndpoint.java:261)\r\n\tat org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.consume(RemoteEndpoint.java:190)\r\n\tat org.eclipse.lsp4j.jsonrpc.json.StreamMessageProducer.handleMessage(StreamMessageProducer.java:192)\r\n\tat org.eclipse.lsp4j.jsonrpc.json.StreamMessageProducer.listen(StreamMessageProducer.java:94)\r\n\tat org.eclipse.lsp4j.jsonrpc.json.ConcurrentMessageProcessor.run(ConcurrentMessageProcessor.java:99)\r\n\tat java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)\r\n\tat java.util.concurrent.FutureTask.run(FutureTask.java:266)\r\n\tat java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)\r\n\tat java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)\r\n\tat java.lang.Thread.run(Thread.java:748)\r\nCaused by: java.lang.reflect.InvocationTargetException\r\n\tat sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)\r\n\tat sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)\r\n\tat sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)\r\n\tat java.lang.reflect.Method.invoke(Method.java:498)\r\n\tat org.eclipse.lsp4j.jsonrpc.services.GenericEndpoint.lambda$null$0(GenericEndpoint.java:65)\r\n\t... 11 more\r\nCaused by: java.lang.IllegalArgumentException\r\n\tat sun.nio.fs.WindowsFileSystem.getPathMatcher(WindowsFileSystem.java:288)\r\n\tat org.javacs.kt.classpath.FindClassPathKt.ignoredPathPatterns(FindClassPath.kt:75)\r\n\tat org.javacs.kt.classpath.FindClassPathKt.workspaceResolvers(FindClassPath.kt:62)\r\n\tat org.javacs.kt.classpath.FindClassPathKt.access$workspaceResolvers(FindClassPath.kt:1)\r\n\tat org.javacs.kt.classpath.FindClassPathKt$findClassPath$resolver$1.invoke(FindClassPath.kt:14)\r\n\tat org.javacs.kt.classpath.FindClassPathKt$findClassPath$resolver$1.invoke(FindClassPath.kt)\r\n\tat kotlin.sequences.FlatteningSequence$iterator$1.ensureItemIterator(Sequences.kt:279)\r\n\tat kotlin.sequences.FlatteningSequence$iterator$1.hasNext(Sequences.kt:267)\r\n\tat org.javacs.kt.classpath.FindClassPathKt.findClassPath(FindClassPath.kt:116)\r\n\tat org.javacs.kt.CompilerClassPath.refresh(CompilerClassPath.kt:13)\r\n\tat org.javacs.kt.CompilerClassPath.addWorkspaceRoot(CompilerClassPath.kt:33)\r\n\tat org.javacs.kt.KotlinLanguageServer.initialize(KotlinLanguageServer.kt:68)\r\n\t... 16 more\r\n"
    }
}

Unfortunately, VSCode's output log also disappears once the language server terminates. The question is thus whether there is a better way to display uncaught exceptions, ideally featuring the stacktrace.

[fwcd]

Will be implemented once https://github.com/eclipse/lsp4j/issues/337 is resolved.