Clarify interactions between wl_surface.leave and wl_output destruction
In this situation:
- Client creates and maps a
wl_surface
- Compositor sends
wl_surface.enter
with an output - Compositor removes the
wl_output
global
Currently wlroots doesn't send wl_surface.leave
events. Some other compositors do (Mutter, KWin). This surprises some client authors: wlroots/wlroots#3559.
We should document whether this is something clients need to handle.