This CL fixes a bug in the tracing of full GC cycles that was introduced
by https://crrev.com/3432211. In doing so, it refactors the tracing of
cycles by introducing an explicit state in GC tracing events, which
follows the phase within the GC cycle as perceived by the tracer. Two
new methods, (Start|Stop)AtomicPause are introduced; together with
(Start|Stop)Cycle they mark the state transitions. The existing methods
(Start|Stop)ObservablePause are now disentangled from cycles and state
transitions.

Bug: v8:12503
Bug: chromium:1154636
Change-Id: Ie4b863bc27f81dd6858103a8988874d89e6e8517
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3440663Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Nikolaos Papaspyrou <nikolaos@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79043}