Multiple windows on one `RawDisplayHandle`

[Fuzzyzilla]

Allow multiple windows. Would need a change to the event system for a notion of which surface a given event belongs too, and even some concepts that aren't exposed like pads being owned by a surface.

On wayland, the same connection is re-usable for every window on the same display object. On ink RTS, a RealTimeStylus is needed per-window.