The concurrent marker can now process all objects.
This patch also eagerly visits the objects that undergo layout
changes. This is because previously such objects were pushed
onto the bailout worklist, which is gone now.
To preserve the incremental step accounting, the patch introduces
a new GC tracer scope called MC_INCREMENTAL_LAYOUT_CHANGE.

Bug: v8:8486
Change-Id: Ic1c2f0d4e2ac0602fc945f3258af9624247bd65f
Reviewed-on: https://chromium-review.googlesource.com/c/1386486
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58712}