Regarding the sequence = 0 fallback: in some cases (moving a cursor
plane on atomic amdgpu) we get sequence = 0 in the page flip callback.
This seems like an amdgpu bug, so work around it by assuming a sequence
delta of 1 (it is equal to 1 because of the sequence != 0 check above).
Sequence can also legitimately be 0 if we're lucky during the 32-bit
overflow, in which case assuming a delta of 1 will give more or less
reasonable values on this and next presentation, after which it'll be
back to normal.
Sequence is also 0 on mode set fallback and when running nested, in
which case assuming a delta of 1 every frame is the best we can do.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1484>
The presentation-time protocol allows surfaces to get accurate
timestamps of when their contents were shown on screen.
This commit implements a stub version of the protocol which correctly
discards all presentation feedback objects (as if the surface contents
are never shown on screen). Subsequent commits will implement sending
the presented events to surfaces shown on screen.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1484>
