Clean up use of frame_signal
This is an effort to eliminate
weston_output, although we still have to decide what to do with
output->previous_damage usage in DRM backend.
1/6. Move the
weston_output_repaint(), what makes the code easier to follow and avoids duplication. This should have no observable effects.
2/6 and 3/6. For users that are listening to
frame_signaland rely on
void *dataparameter to be a pointer to
weston_outputmember to their private data structs. This way we can make
previous_damageto be given using this data parameter.
4/6. Change the
frame_signalemit call to pass damage region as the data argument.
5/6 and 6/6. Change the
output->previous_damageto instead get the damage from the
Fixes: #256 (closed)