With Cage becoming more popular since its mention on Phoronix and
therefore getting more use-cases than just my own project, add XWayland
support. The refactoring of 2cf40f7 makes this much easier. Note that
this is a no-cost addition for those of us not using XWayland as it is a
compile-time option that needs to be explicitly enabled by adding
`-Dxwayland=true` to your meson command.
This makes Cage much easier to maintain. Not only is it easier where to
look and to maintain a mental model of the code, there is also more
encapsulation, better abstractions and better extendability.
Since we do not ever minimize or otherwise unmap clients (except when
destroying them), we don't need to track mapped/unmapped state. The
destroy case is captured in checking whether the surface has a buffer
attached to it, before requesting its texture.
This makes it easier to extend in the future. Also, it will make it
easier to add (un)install targets and eventually, distribute files such
as systemd services.
It appears that wlr_xdg_toplevel_set_maximized does not actually change
the size of the surface. Rather, it only makes the surface think it is
maximized. Hence, we need to set the size to that of the output
manually.
