Provide a way to trigger a write barrier when updating the embedder
fields. In future, such a mechanism should be encapsulated into V8.

Bug: chromium:1056170
Change-Id: I4e43362993c3e58d5bebdd58a7d46a39c0aa4f06
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2640419Reviewed-by: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72227}