The concurrent marker can now visit maps and mark the subset of
descriptors that a map requires.

Bug: v8:8486
Change-Id: I184442ec90a8f60c73cfe16d6e9d66f4efa92a01
Reviewed-on: https://chromium-review.googlesource.com/c/1384320
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58466}