With shared GCs we need to stop all isolates in a safepoint. But in
some cases not every main thread of each isolate is able to reach a
safepoint. We need to park the main thread manually here in d8.

Bug: v8:11708
Change-Id: I45d495cecce92ebef7e25ff16ea852430f3645e5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3456023
Auto-Submit: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79067}