[heap] Explicitly skip write barriers during WeakCell processing

This CL explicitly skips implicit write barriers during WeakCell
processing in minor and major GCs, and relies on explicit barriers
by the GC where/when needed.

The CL also introduces `SKIP_WRITE_BARRIER_FOR_GC` that allows to
disable write barriers during the GC atomic pause even if they would
otherwise be needed.

Bug: 340777103
Change-Id: Ie821744a66ed717b938f7cc56545505eb7928f12
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/6990433
Auto-Submit: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#102992}