Finishing an operation started via
`OngoingOperationTracker.BeginOperation()` was risky in cases where the
operation ended at a callback on another thread (which, in the case of
multiplayer, is *most* cases). In particular, if any consumer registered
a callback that mutates transforms when the operation ends, it would
result in crashes after the framework-side safety checks.
Rework `OngoingOperationTracker` into an always-present component
residing in the drawable hierarchy, and ensure that the
`operationInProgress` bindable is always updated on the update thread.
This way consumers don't have to add local schedules in multiple places.
It needs to be explicitly stated that the users in this list are related
to the *joined* room. Especially since it's sharing its variable name
with `SpectatorStreamingClient` where it has the opposite meaning (is a
list of *globally* playing players).
The fix here is correcting the access of `user.Country`. The deicision
to have null users display is because this is the best we can do (if
osu-web could not resolve the user). We still want the users in the
lobby to be aware of this user's presence, rather than hiding them from
view.
osu-stable does a similar thing, showing these users as `[Loading]`. I
decided to go with blank names instead because having *any* text there
causes confusion. We can iterate on this in future design updates.