[runtime] Fix conserving stack trace when re-throwing marshalled exceptions. Fixes #19417. (#20316)

The stack trace from unhandled exception is now:

    Unhandled managed exception: Index was out of range. Must be non-negative and less than the size of the collection. (Parameter 'index') (System.ArgumentOutOfRangeException)
       at System.Collections.Generic.List`1[[System.String, System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].get_Item(Int32 index)
       at CrashiOS.RootViewController.GetItem() in /Users/rolf/test/bugs/StackTraceIssue/CrashiOS/RootViewController.cs:line 19
       at CrashiOS.RootViewController.<.ctor>b__1_0(Object _, EventArgs _) in /Users/rolf/test/bugs/StackTraceIssue/CrashiOS/RootViewController.cs:line 12
       at UIKit.UIBarButtonItem.Callback.Call(NSObject sender) in xamarin-macios/src/UIKit/UIBarButtonItem.cs:line 33
    --- End of stack trace from previous location ---
       at ObjCRuntime.Runtime.ThrowException(IntPtr gchandle) in xamarin-macios/src/ObjCRuntime/Runtime.cs:line 2655
       at UIKit.UIApplication.UIApplicationMain(Int32 argc, String[] argv, IntPtr principalClassName, IntPtr delegateClassName) in xamarin-macios/src/UIKit/UIApplication.cs:line 64
       at UIKit.UIApplication.Main(String[] args, Type principalClass, Type delegateClass) in xamarin-macios/src/UIKit/UIApplication.cs:line 96
       at Program.<Main>$(String[] args) in /Users/rolf/test/bugs/StackTraceIssue/CrashiOS/Main.cs:line 26

as opposed to:

    Unhandled managed exception: Index was out of range. Must be non-negative and less than the size of the collection. (Parameter 'index') (System.ArgumentOutOfRangeException)
       at ObjCRuntime.Runtime.ThrowException(IntPtr gchandle)
       at UIKit.UIApplication.UIApplicationMain(Int32 argc, String[] argv, IntPtr principalClassName, IntPtr delegateClassName)
       at UIKit.UIApplication.Main(String[] args, Type principalClass, Type delegateClass)
       at Program.<Main>$(String[] args) in /Users/rolf/test/bugs/StackTraceIssue/CrashiOS/Main.cs:line 26

Fixes https://github.com/xamarin/xamarin-macios/issues/19417.

runtime/runtime.m

@@ -2279,10 +2279,30 @@ xamarin_process_nsexception_using_mode (NSException *ns_exception, bool throwMan
 		GCHandle handle;
 		if (exc_handle != NULL) {
 			GCHandle e_handle = [exc_handle getHandle];
+			GCHandle rethrow_exception_gchandle;
 			MONO_ENTER_GC_UNSAFE;
+
+			//
+			// We want to maintain the original stack trace of the exception, but unfortunately
+			// calling mono_runtime_set_pending_exception directly with the original exception will overwrite
+			// the original stack trace.
+			//
+			// The good news is that the managed ExceptionDispatchInfo class is able to capture
+			// a stack trace for an exception and show it later.
+			//
+			// The xamarin_rethrow_managed_exception method will use ExceptionDispatchInfo
+			// to throw an exception that contains the original stack trace, we will then capture that
+			// exception, and pass it to mono_runtime_set_pending_exception.
+			//
+			xamarin_rethrow_managed_exception (e_handle, &rethrow_exception_gchandle);
+			if (rethrow_exception_gchandle == INVALID_GCHANDLE) {
+				PRINT (PRODUCT ": Did not get a rethrow exception, will throw the original exception. The original stack trace will be lost.");
 				MonoObject *exc = xamarin_gchandle_get_target (e_handle);
 				handle = xamarin_gchandle_new (exc, false);
 				xamarin_mono_object_release (&exc);
+			} else {
+				handle = rethrow_exception_gchandle;
+			}
 			MONO_EXIT_GC_UNSAFE;
 		} else {
 			handle = xamarin_create_ns_exception (ns_exception, &exception_gchandle);