ShouldFinalize should only be called if major incremental marking is
active, and can crash if minor incremental marking is active, if
MajorMC's local_marking_worklists_ was reset.

The only caller is IsMarkingComplete. This CL changes the IsMarking
check to IsMajorMarking to solve this issue, and renames
IsMarkingComplete to IsMajorMarkingComplete.

Bug: v8:13012
Change-Id: Iba6bd5b7977ec8566c3ab0f047646d8cafd45038
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3879485
Commit-Queue: Leon Bettscheider <bettscheider@google.com>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#83064}