This CL adds verification of the old-to-shared remembered set to
--verify-heap. During shared GCs client heaps will be scanned for
references into the shared heap, this CL will CHECK that every found
slot is contained in the old-to-shared remembered set. After this
gets a bit more stable, the full heap iteration can be dropped and we
can fully rely on the remembered set instead.

Bug: v8:11708
Change-Id: I0b5c4edfe3271306e4e7af7394472534113e1953
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3792605Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82578}