No yielding is necessary since the main thread Join()s.

max concurrency is determined based on either
remaining_memory_chunks_ or global pool size
(copied_list_ + promotion_list_)

Change-Id: Ie30fa86c44d3224b04df5d79569bce126ce7d96b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2354390
Commit-Queue: Etienne Pierre-Doray <etiennep@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69746}