protocol: make it clear wl_surface.enter/leave are not for frame throttling
Some clients rely on wl_surface.enter/leave to start/stop their rendering loop.
There are cases where this doesn't work:
- Some compositors don't send wl_surface.leave when a toplevel is hidden. For instance Sway doesn't send this event when a toplevel is on an inactive workspace (but doesn't send wl_surface.frame events).
- Some compositors might still want applications to continue to render even if away from outputs. For instance a compositor that allows to screen record individual toplevels might not send a wl_surface.enter event for hidden toplevels.
Signed-off-by: Simon Ser firstname.lastname@example.org