scene: send surface enter/leave events, add primary output, add wlr_scene_send_frame_done()

This enhances wlr_scene_render_output() and wlr_scene_output_commit() to call wlr_surface_send_frame_done() and optionally wlr_presentation_surface_sampled_on_output() for rendered surfaces.

This makes it easier for compositors to properly send frame done events and presentation feedback by adding a primary output field to wlr_scene_surface.