Recompute heap limits while all threads are still stopped. Otherwise
setting the limits races with concurrent background threads performing
allocations.

Bug: v8:10315
Change-Id: I17e711b960e1fde05adb4f4b794f813b94190ef1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2157375Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67280}