waylandsink: Ensure correct mapping of area_surface
If the area_surface got unmapped when changing to the READY or
NULL state, we currently don't remap it when playback resumes and
wp_viewporter is supported. Without wp_viewporter we do remap
it, but rather unintentionally and also when not wanted.
On Weston this has not been a big problem as it so far wrongly maps
subsurfaces of unmapped surfaces anyway - i.e. only the black
background was missing on resume. On other compositors and future
Weston this prevents the video_surface to get mapped.
Shuffle things around to ensure area_surface is mapped in the
right situations and do some minor cleanup.
See also wayland/weston#426 (closed)
CC @ndufresne
Includes and depends on !1446 (merged)
This would be good to backport to 1.20, with or without the cleanups.