compositor-wayland: Flush the display on commit
compositor-wayland: Flush the display on commit

This fixes the problem where animations will wait to play until input is
received.  In general, it also makes the backend far more responsive.

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>

https://bugs.freedesktop.org/show_bug.cgi?id=68221

Tarnyko/weston-xdg_surface_present,Fantu/compositor-spice,Fantu/compositor-spice,udoprog/weston,Tarnyko/weston-xdg_surface_present,xorgy/weston,eyolfson/weston,jonnylamb/weston,sir-murray/weston,Gnurou/weston,giucam/weston,mchalupa/weston,eyolfson/weston,Fantu/compositor-spice,udoprog/weston,krezovic/weston,sir-murray/weston,kwm81/weston,krezovic/weston,kwm81/weston,Gnurou/weston,jonnylamb/weston,mchalupa/weston,giucam/weston,xorgy/weston