WorkerThreads access the queue to get new tasks, that's why all of
them need to stop before we can destroy the queue.

This hopefully fixes the linked race/crash since I can't reproduce
this locally.

Bug: v8:12914
Change-Id: Icbfd462f106a4a1f0bbd525f0b7f342e9857a539
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3672421Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80841}