Previously if we had no measurements then `compute_max_render_time_us`
would pessimise its answer to ensure triple buffering could be reached:
if (frame_clock->state >= CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE)
ret += refresh_interval_us;
But that also meant entering triple buffering even when not required.
Now we make `compute_max_render_time_us` more honest and return failure
if the answer isn't known (or is disabled). This in turn allows us to
optimize `calculate_next_update_time_us` for this special case, ensuring
triple buffering can be used, but isn't blindly always used. So when
TIMESTAMP_QUERY support is missing we now take the same path as if
presentation timestamps are missing (introduced in 56fc09151d and
improved in 0555a5bbc1), which has the benefit of naturally switching
from double to triple buffering as required without actually having to
measure render times.
This makes a visible difference to the latency when dragging windows in
Xorg, but will also help Wayland sessions on platforms lacking
TIMESTAMP_QUERY such as Raspberry Pi.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1441>
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