It's locked exclusively in the MapUpdater API methods, and locked
shared in ComputePropertyAccessInfo (CPAI).

This lock is a step towards running CPAI on background threads. The
simple lock portion is landed separately in this CL to get an early
signal on potential lock overhead perf impact.

The lock is implemented and used very conservatively at the moment:

- it's a single global lock (and not e.g. per-map).
- it's locked for the entire method call duration (instead of only in
  relevant parts).

Both points can potentially be improved in the future.

Bug: v8:7790
Change-Id: I073423497e01b4901101973387a19962f953a576
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2797286Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73773}