feat: add resuming state to room events

[holzgeist]

I want to give users feedback about network events ASAP. Currently, if network access is temporarily lost, the first event that gets emitted is a Reconnected event. Having access to the internal Resuming event, we can show the users that something is up. This should help to avoid repeated "Hello? Can you hear me?" that nobody will ever hear ;)

WDYT?