We can check map validity cells for Sminess without checking their
value, since their value as a Smi (and not a Cell) should always be
"valid"

Change-Id: Ie73079107144e352c358c0ec42abd0c10bdcf73a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3663090
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80721}