This field has been used with atomically relaxed semantics due to a race
with layout_descriptor [1]. Even though layout_descriptor doens't exist
anymore, this race is still present presumably because the transition to
a new map happens on StoreIC. We can set it as atomic for non-cm and
atomic relaxed for cm like we did with the other Map's fields.

Note that originally, this field was relaxed so we are reverting it
back to what it was for concurrent marking.

[1]: https://chromium-review.googlesource.com/c/v8/v8/+/555210/

Bug: v8:7790, v8:11696
Change-Id: I5d8c18bedb84b4bd5dc771e87310bc14409cfed8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2874454Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74386}