Add histogram for time-to-collection. As a drive-by change also
move CollectionBarrier into its own class and rename V8.TimeToSafepoint
to V8.StopTheWorld such that the histogram name and the trace file entry
now have the same name.

Bug: v8:10315
Change-Id: I86e2a9592d10316d04bc8cab37ff548067aadf78
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2465840Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70489}