libs: wayland: add support for XDG-shell protocol

libs: wayland: add support for XDG-shell protocol

[wl_shell] is officially [deprecated], so provide support for the
XDG-shell protocol should be provided by all desktop-like compositors.
(In case they don't, we can of course fall back to wl_shell).

Note that the XML file is directly provided by the `wayland-protocols`
dependency and generates the protocol marshalling code.

[wl_shell]: https://people.freedesktop.org/~whot/wayland-doxygen/wayland/Client/group__iface__wl__shell.html
[deprecated]: https://github.com/wayland-project/wayland/commit/698dde195837f3d0844b2725ba4ea8ce9ee7518c