We can't use gdk_display_get_pointer/gdk_window_get_pointer from gjs
when XKB is active. We already had a wrapper that did the
get-modifier-state part of that, but some places also need the
get-pointer-location part of it. So update our wrapper to return both,
and update js code to use it.
https://bugzilla.gnome.org/show_bug.cgi?id=613428
d42263c1bc