MinorMC events were incorrectly grouped under the V8.GCScavenger trace event name.

This CL introduces the trace event name V8.GCMinorMC and uses it when MinorMC is used instead of Scavenger.

Change-Id: Ide22526adfa9cc6dec91d3c34186b1c2ea6eb862
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3717989
Commit-Queue: Leon Bettscheider <bettscheider@google.com>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81323}