Move logic to perform a global safepoint into GlobalSafepointScope
respectively GlobalSafepoint for easier reuse of this functionality in
the future.

Note that full functionality for a global safepoint will be provided
in a subsequent CL.

Bug: v8:11708
Change-Id: I80dd22c36ab01df573623aa36ead9cc373663b9b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3259531Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77719}