The instance type is set before setting the map inside an Object. It
is relaxed and not non-atomic to prevent a false positive TSAN failure
(see https://chromium-review.googlesource.com/c/v8/v8/+/2682641).

Bug: v8:7790
Change-Id: Iddd28ffb06b5a882e77c4bf88bf8580df792f198
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2773042Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73570}