This class is intended to be used as a base class for D-bus interface
implementations that deal with "session" objects, i.e. a D-Bus object
representing a certain session of some kind, e.g. a screen cast session.
It handles things such as hooking up to the D-Bus client watcher,
generates IDs, handles shutdown procedures.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2713>
