RunSingleMicrotask calls Runtime::ReportMessage, but the implementation
of ReportMessage would unconditionally discard these exceptions. This
CL removes all of the intermediate logic and directly calls
MessageHandler::ReportMessage, restoring the ability of
RunSingleMicrotask to report exceptions that occur in microtasks.

Bug: v8:8326
Change-Id: I493de74383b2ab191d786611fb9eba9d27e7a243
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2162121
Commit-Queue: Gus Caplan <me@gus.host>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67630}