wayland/xdg-shell: Do not maximize if not possible

On X11, if a window cannot be maximized because its minimum size is already larger than the output size, a request to maximize will be ignored.

On Wayland, however, we would still honor the maximize request and switch the window state to maximized, without actually moving the window which leads to weird visual effects, as the window end up being maximized in-place.

To avoid this, make sure the window has the maximize functionality available prior to change its state in xdg-shell set_maximized request.

Closes: #463 (closed)