* Map may be forwarded here, so use IsMapOrForwardedMap in DCHECK
* Code didn't expect a slot in the map word.

Bug: v8:12578
Change-Id: I8dd9cd57fb1336e0014812b7a2e35dc209f78a2c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3429292Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78915}