This removes all EGL-specific code from the wayland backend.
Notable unresolved question: due to wayland design, the resizing
methods will only get/set the size of the drawn borders, not of the
actual content drawn. This latter size cannot be controlled by winit.
Integrate with wayland-window crate to draw decorations
allowing resize & move of the window.
Leaving the wayland backend as disabled until full usability
is ensured.
