presentation_feedback: add the sampled state
cc https://github.com/swaywm/sway/issues/4451
The idea is that feedback goes from nothing to committed to either sampled (and subsequently presented) or discarded.
Sway patch: https://github.com/swaywm/sway/pull/4465
Compositor maintainers: call wlr_presentation_surface_sampled
when rendering a surface.