Fix 2FA verification via link not working correctly

Closes ppy#26835.

I must have not re-tested this correctly after all the refactors...

Basically the issue is that the websocket connection would only come
online when the API state changed to full `Online`. In particular
the connector would not attempt to connect when the API state was
`RequiresSecondFactorAuth`, giving the link-based flow no chance to
actually work.

The change in `WebSocketNotificationsClientConnector` is relevant in
that queueing requests does nothing before the API state changes to full
`Online`. It also cleans up things a bit code-wise so... win?

And yes, this means that the _other_ `PersistentEndpointClientConnector`
implementations (i.e. SignalR connectors) will also come online earlier
after this. Based on previous discussions
(ppy#25480 (comment)) I think
this is fine, but if it is _not_ fine, then it can be fixed by exposing
a virtual that lets a connector to decide when to come alive, I guess.

Author: bdach

osu.Game/Online/Notifications/WebSocket/WebSocketNotificationsClientConnector.cs

@@ -29,14 +29,11 @@ public WebSocketNotificationsClientConnector(IAPIProvider api)
 
         protected override async Task<PersistentEndpointClient> BuildConnectionAsync(CancellationToken cancellationToken)
         {
-            var tcs = new TaskCompletionSource<string>();
-
             var req = new GetNotificationsRequest();
-            req.Success += bundle => tcs.SetResult(bundle.Endpoint);
-            req.Failure += ex => tcs.SetException(ex);
-            api.Queue(req);
-
-            string endpoint = await tcs.Task.ConfigureAwait(false);
+            // must use `PerformAsync()`, since we may not be fully online yet
+            // (see `APIState.RequiresSecondFactorAuth` - in this state queued requests will not execute).
+            await api.PerformAsync(req).ConfigureAwait(false);
+            string endpoint = req.Response!.Endpoint;
 
             ClientWebSocket socket = new ClientWebSocket();
             socket.Options.SetRequestHeader(@"Authorization", @$"Bearer {api.AccessToken}");

osu.Game/Online/PersistentEndpointClientConnector.cs

@@ -69,6 +69,7 @@ private async Task connectIfPossible()
                     break;
 
                 case APIState.Online:
+                case APIState.RequiresSecondFactorAuth:
                     await connect().ConfigureAwait(true);
                     break;
             }
@@ -83,7 +84,7 @@ private async Task connect()
 
             try
             {
-                while (apiState.Value == APIState.Online)
+                while (apiState.Value == APIState.RequiresSecondFactorAuth || apiState.Value == APIState.Online)
                 {
                     // ensure any previous connection was disposed.
                     // this will also create a new cancellation token source.