Concurrent marking jobs were only joined in Heap::TearDown and
therefore may still update counters while DumpAndResetStats() emits
stats.

This CL stops concurrent marking tasks in Heap::StartTearDown when
also stopping other concurrent tasks like sweeping or unmapping of
pages.

Bug: v8:13175, v8:12775
Change-Id: Iccddbfce5e30002e0db63ba0bdea5ea6b2d5cc40
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3827869Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82849}