QueryUpdateEmitter should return a number of affected queries

[m1l4n54v1c]

Currently, when emitting an update or (exceptionally) completing the QueryUpdateEmitter we don't get any information back. It would be beneficial to get the number of affected subscription queries.

This information could help us to detect scenarios where subscription queries are being delayed. Retrying an emit/complete in these scenarios might help.

[smcvb]

We've had some internal discussion on this issue whether it's really what we should be going for, as it couples the emitting side with the query dispatching side. To not obstruct our 4.4. release, we will be postponing this issue 'til 4.4.1.