Make sure gnome-shell gets notified of errors that happen during screen
recording using the screencastService, so that it can properly notify the
user about the error and tear down its state, too.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2752>
We'll soon move the inlined XML of all interfaces we export or consume into
separate files. That's a significant increase from the interfaces for which
we install documentation, so it makes sense to use a dedicated subdir.
https://gitlab.gnome.org/GNOME/gnome-shell/issues/537