EmbedderStackStateScope is used to disable conservative stack scanning
for cppgc when the stack is known to not contain heap pointers. Also,
DisableConservativeStackScanningScopeForTesting is used to disable CSS
for the V8 heap in tests that assume a precise GC. Until now, these two
have used two different mechanisms for disabling CSS. This CL merges
the two mechanisms and implements the latter scope via the former.
This is a reland of commit f51e0bb1db
reviewed on https://chromium-review.googlesource.com/c/v8/v8/+/4111954
Bug: v8:13257
Change-Id: Ia124a4201686e0ea79f9cd07bc3888b9781cafa9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/4128141
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Nikolaos Papaspyrou <nikolaos@chromium.org>
Cr-Commit-Position: refs/heads/main@{#85066}
15c726bd63