It relied on indices in arrays determining tile direction and
non-obvious bitmask logic to translate to _GTK_EDGE_CONSTRAINTS. Change
this to explicitly named edge constraints, and clear translation methods
that converts between mutters and GTK+s edge constraint formats.
As with xdg-toplevel, a gtk-surface can be unmanaged by the compositor
without the client knowing about it, meaning the client may still send
updates and make requests. Handle this gracefully by ignoring them. The
client needs to reset all the state anyway, if it wants to remap the
same surface.
https://gitlab.gnome.org/GNOME/mutter/issues/240
Following up the previous patch, this patch makes the
Wayland backend send the edge constraints through a
custom protocol extension internal to GTK.
As it mature, we can think of upstreaming the protocol
to Wayland itself.
https://bugzilla.gnome.org/show_bug.cgi?id=751857
