When iterating slots for promoted objects we now also need to visit
the map word slot since maps might get compacted. If we do not do this,
we risk losing the already recorded slot for the map word in case that
object already got marked.

Bug: v8:12578, chromium:1295239
Change-Id: I34fbf7ae4b9e36eae8e7e3df354b5fd19adcb08f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3448373Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79006}