Background threads use a new mechanism to request a GC from the main
thread. Previously they used MemoryPressureNotification to request the
collection. However this conflicts with the embedder's usage of
MemoryPressureNotification.

Bug: v8:10315
Change-Id: Ib25a13a43e1f6a8785bb0d421dd056ae06a4a350
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2429270Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70249}