This CL adds missing locks to the PersistentRegions for
(Weak)CrossThreadPersistents.
To make sure no locks are missed in the future, this CL also splits
PersistentRegion and introduces CrossThreadPersistentRegion that checks
whether a lock is taken whenever it is accessed.

Bug: chromium:1056170
Change-Id: Iaaef4a28af0f02bcb896706e9abf1ee5ad2ee1e1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2737299
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73264}