I'm tired of xwayland crashing and killing my shell.

Focus active

Closes #2390

See merge request GNOME/gtk!2324

Use the new GTK_CROSSING_ACTIVE crossing events to update
the im context focus when the window becomes active or
inactive. IBus requires this, since it has only a single,
global focus location.

Fixes: #2390

Emit crossing events when the active window changes.
We don't want to emit GTK_CROSSING_FOCUS events, since
every window has its own focus location (focus does not
jump from window to window), so we use the new
GTK_CROSSING_ACTIVE type of crossing event for this.

Document the different crossing event kinds that we use,
and add GTK_CROSSING_ACTIVE. We are going to use it in
the future when the active window changes.

More device API cleanup

See merge request GNOME/gtk!2323

We don't want to tell what they are, and the distinction is now less
clear. Remove the adjective from the function name.

There is no longer a hierarchy of devices, or none that is seen
on the outside.

The only legit uses of device types are here in gdk/x11, move the
concept of device type to X11, so we can drop it from public API.