Add Bonjour/Zeroconf service discovery APIs
Now that Avahi has an API which can be effectively used over D-Bus without races, it should be possible to add API to GIO so it can do service discovery.
This could in turn be used to implement service discovery in xdg-desktop-portal, which could be filtered on the portal side (eg. Rhythmbox could request access to
_daap._tcp and only get access to those services, and nothing else).