Previously, only root marking performed during the final pause
was accounted for in the tracing data.

This CL enables tracing of the initial root marking step of MajorMC.

Change-Id: I4aa8a52144d81a12e43a481518acbab118978992
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3724793
Commit-Queue: Leon Bettscheider <bettscheider@google.com>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81378}