[heap] Make stress_concurrent_allocation more resilient against OOM

Allow all allocations to fail in StressConcurrentAllocatorTask, this
still stresses the concurrent allocation code path but makes
--stress-concurrent-allocation more resilient against OOM. In case the
allocation fails try to start a GC.

Bug: v8:9337
Change-Id: I3633687d67d3a135114a3ea46b5238378153f377
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2797280


Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73802}