Update scope names to match the new scope naming scheme we settled on.
This CL also:
1) Adds high-level scopes for atomic mark/sweep/compact and incremental
   mark/sweep.
2) Remove scopes that will now become redundant (i.e. SweepAndCompact,
   UnifiedMarkingStep, etc.)

The new scopes are no longer aligned with the existing telemetry code
(gc_metric.html) in blink.

Bug: chromium:1056170
Change-Id: I510269e24172f411b2a98c0a0a250a6e9fe58841
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2563882
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71480}