It turns out that accerciser depends on this undocumented
method that is not in the xml at all, otherwise interface
sections in the accerciser ui never get enabled.
And generate the code for the DBus interfaces.
We don't want the full object manager experience, here, because we're
going to have a single object responding to various interfaces and
remote method calls. For this reason, we're not using the gnome module
in Meson to call gdbus-codegen for us: we need to use the interface info
command line arguments, and those are not available from Meson.
