1. In ElementAccessFeedback::HasOnlyStringMaps - we can assume
  the map is safe to read because it was read earlier from the
  feedback vector and passed the gc predicate then.
2. In JSHeapBroker::GetPropertyAccessInfo - we can assume that the
  feedback vector in a FeedbackSource is store-ordered/safe to read.

Bug: v8:7790, v8:12282
Change-Id: Ie09acdfaac3d5e767ffe74e4bad941d4eeb47f9a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3200082
Commit-Queue: Michael Stanton <mvstanton@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77213}