Add GroupCallEventHandlerEvent.Room (#2631)
* Add GroupCalEventHandlerEvent.Room
Emit an event when the group call event handler has processed all
pending group calls.
* Remove unused return value
* Add void return type
Co-authored-by: Šimon Brandner <simon.bra.ag@gmail.com>
Co-authored-by: Šimon Brandner <simon.bra.ag@gmail.com>
