This reverts commit 92f815a8.

Reason for revert: broke tests; see https://ci.chromium.org/p/v8/builders/ci/V8%20Linux64%20TSAN/33395?

Original change's description:
> Reland "[Heap] ScavengerCollector use Jobs."
>
> 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/+/2399041
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Commit-Queue: Etienne Pierre-Doray <etiennep@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#70135}

TBR=ulan@chromium.org,etiennep@chromium.org

Change-Id: I4823c642546b82a9a9c8955151cd8784e4b86bc8
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2431551
Commit-Queue: Francis McCabe <fgm@chromium.org>
Reviewed-by: Francis McCabe <fgm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70138}