In certain scenarios, the frame clock needs to handle present feedback
long before the assumed presentation time happens. To avoid scheduling
the next frame to soon, avoid scheduling one if we were presented half a
frame interval within the last expected presentation time.
https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1285
This adds a current unused, apart from tests, frame clock. It just
reschedules given a refresh rate, based on presentation time feedback.
The aiming for it is to be used with a single frame listener (stage
views) that will notify when a frame is presented. It does not aim to
handle multiple frame listeners, instead, it's assumed that different
frame listeners will use their own frame clocks.
Also add a test that verifies that the basic functionality works.
https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1285
