notification: Use snap name and app name as fallback desktop-entry
notification: Use snap name and app name as fallback desktop-entry

Snaps use desktop IDs based on the snap name and the application name
inside the snap, so if we're in a such container, we need to compute the
desktop-entry using those values. We can figure them out from the snap
cgroup they're in.

In such case, don't even try to use the GApplication ID as that is
likely wrong in a snapped environment.

GNOME/libnotify,GNOME/libnotify