The `GetWindows` method gives access to the list of windows for each
application with some of their properties, so utilities such as dogtail
can pick the window of their choice to interfere with using the provided
window id.
https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/326
Add a D-Bus API that allows the API user to introspect the application
state of the shell. Currently the only exposed information is list of
running applications and which one is active (i.e. has focus).
https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/326