This replaces VisitMode with a set of option flags that allow skipping
specific roots like unserializable, weak, global handles, etc.
The advantage is that it is no longer coupled with the callers and does
not know about different types of GCs and their phases.

The CL is pure refactoring without behavior changes except for the
heap verification where more roots are verified that before.

Change-Id: I350b2ed14826e0efb75770111c6b28bb8d4d9845
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2190420Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67704}