Locks the allocation mutex if SupportsConcurrentAllocation() returns
true. Unifies code/condition from multiple usages.

Bug: v8:10315
Change-Id: I684d12284e862df5d68986841e04ff25527422eb
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2352775
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69379}