Render software cursors in compositor
This PR removes wlr_output_set_fullscreen_surface
, adds a new wlr_output_render_software_cursors
helper, and removes the 180 damage flip in wlr_output_swap_buffers
(which is GL-specific).
This also fixes frame events for hardware cursors, which were sent too soon.
While this improves the situation, this doesn't completely fix #1363, because redesigning how cursor surfaces are handled and how output damage is managed requires more thought.
See #1363