During a shared GC we need to iterate the twice: for marking and later
when updating pointers after evacuation. This CL introduces a new
remembered set to avoid the second heap iteration, the remembered set
is created when iterating the client heaps for marking. When updating
pointers, the GC only needs to visit slots in the remembered set.
CLIENT_TO_SHARED is only used during GC atm.

Bug: v8:11708
Change-Id: Ie7482babb53b5f6ca2115daafe6f208acae98d6e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3315443Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78332}