This is a reland of commit c3a5c5b1

The previous CL was writing into the wrong sets when invoking
CollectSlots<OLD_TO_SHARED>(). Also move the NULL checks out of
that condition to also check this for chunks in the young generation.

Original change's description:
> [heap] Ensure all old-to-shared slots are recorded
>
> 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/+/3792605
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#82578}

Bug: v8:11708
Change-Id: I24b7787977f06708efb7a017dd1ec72f78d0ea13
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3841570Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82653}