This unifies marking worklists handling by the main thread marker and
by the concurrent markers. A new class called MarkingWorklistsHolder
owns all marking worklists: the default worklist, the on-hold worklist,
and the embedder worklist. Each thread creates a local view of the
marking worklists by creating an instance of MarkingWorklists.

Additionally, marking visitors now work on MarkingWorklists instead of
accessing each worklist individually.

Besides cleaning the code up, this CL provides a bottleneck for
implementing per-context worklists.

Bug: chromium:973627
Change-Id: I52ad65c94bc0695287ba7bf4d8a814a9035e2888
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1941947Reviewed-by: Hannes Payer <hpayer@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65421}