GTK windows don't have their tiling states really
hooked into the client-side decoration code, and
the only effect it has is disabling the resizing
edges.

With the introduction of per-edge tiling information,
we are backed by much more precise data on how the
window manager wants the app to behave.

This patch, then, fixes GtkWindow to take into account
per-edge tiling information. For compatibility purposes,
the previous tiled field was kept, and thing will just
continue working if no edge information is supplied.

https://bugzilla.gnome.org/show_bug.cgi?id=783669