This is a reland of 9e8c54f8
Safe to reland as-is with fix in AcquireTaskId
https://chromium-review.googlesource.com/c/v8/v8/+/2401964

Additional changes are made in the reland:
-TRACE_GC is be split for background/foreground scope.
-New IndexGenerator is used for dynamic work assignement.

Original change's description:
> [Heap] ScavengerCollector use Jobs.
>
> 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}

Change-Id: Id9d7a5bf3b2337ae4cf1e76770f4b14ebb8ca256
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2399041Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Etienne Pierre-Doray <etiennep@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70135}