This replaces the DISPATCHED state with new sub-states that are possible
with triple buffering:
DISPATCHED_ONE: Double buffering
DISPATCHED_ONE_AND_SCHEDULED: Scheduled switch to triple buffering
DISPATCHED_ONE_AND_SCHEDULED_NOW: Scheduled switch to triple buffering
DISPATCHED_ONE_AND_SCHEDULED_LATER: Scheduled switch to triple buffering
DISPATCHED_TWO: Triple buffering
Triple buffering is currently disabled until the test cases get updated to
handle it in the next commit.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1441>
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