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
