- Public channels (and announcements) are now alphabetically ordered.
- Private message channels are now ordered by most recent activity.
Closes https://github.com/ppy/osu/issues/30835.
Though the code appears slightly different, it should be semantically
equivalent. APIUser equality is implemented on `Id` and `Host` should
never transition from non-null to null.
This one is super duper annoying to test, because we already have e.g.
`TestScenePlaylistsScreen`. The only way to test it would be to use an
`OsuGameTestScene`.
Maybe this is okay?