Instead of calling it through `BaseRoomInfo::calculate_room_name`.

…rs, not joined+invited

The previous code would use `ACTIVE` which means "either joined or
invited" members, but the code thereafter considered this to be the
number of joined members.

Also replaced a call to `self.members()` (which does a lot of work under
the hood) with a call to `self.joined_user_ids()`, since we only
retrieve the `.len()` of the resulting vector.

… it's used

Since this is a good place where to recompute the cached display name at
start.

…chers

… computed_ in the cached one

… way

The test looks at updates of `RoomInfo`s, but these depends on external
factors like the server sending them in one part or multiple ones.

Instead of trying to figure out which partial updates the server sent,
wait for the stream of `RoomInfo`s to stabilize by trying to get the
latest item from the stream, then wait up to N seconds for another item
to show up, and continue as long as items come in.

This should allow us to get rid of some code that was required to
prevent flakey updates.

…he cached display name in RoomInfo

So revert a few changes to make some functions async, etc.

…c methods

It's not perfect, but it's honest work.