The API allows for querying
- IsAllocationAllowed: Certain GC phases prohibit allocation which can
  be queried; Should be mostly used for debugging checks.
- IsMarking: Allows for querying whether the garbage collector is
  currently marking.

Bug: chromium:1056170
Change-Id: I20ba5fb5be9de6694e8418fa885920eb04bd75ad
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2649257
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72359}