In Isolate::UnwindAndFindHandler(), the thread-in-wasm flag was set
before the destructor of some objects in that function got executed,
e.g. the destructor of {WasmCodeRefScope}. On Windows-asan, these
destructors could throw exceptions (asan on Windows uses exceptions for
its memory access tracking), which get handled initially by the wasm
trap handler, and would thereby invalidate the thread-in-wasm flag.

With this CL a new scope gets introduced which makes sure that setting
the thread-in-wasm flag is the last thing that happens in
Isolate::UnwindAndFindHandler().


Bug: chromium:1195595
Change-Id: If9f5f486c55b3bc2718a1d5aee3e3bd290d0ff35
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2817598
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73904}