Introduce LivenessBroker which is a temporary broker object to expose
liveness during specific garbage collection phases.

This broker can be used to handle:
- PreFinalizer
- Custom weak callbacks
- Internal weak callbacks used for WeakMember

Change-Id: I3870c2b89b2538f04feabf2eb7a4676ce2fe7d61
Bug: chromium:1056170
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2144059Reviewed-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@{#67107}