presentation-shm: Allow setting of delay before surface.commit

presentation-shm: Allow setting of delay before surface.commit

A new optional parameter "-d msecs" allows to specify a
delay before the surface attach/damage/commit to shift
the point in time when a surface update is committed.

This allows to test how different client timings interact
with the compositors repaint timing.

Suggested by Pekka Paalanen.

Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
v2: Clarify the intent, doing a delay in window_create_feedback()
    is a bit surprising. Use nanosleep() instead of clock_nanosleep(),
    which may not support the chosen presentation clock.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>