Refactor the way group calls hang up (#3234)

* Refactor how group call end calls

We previously used disposeCall to terminate the call which meant that
sometimes a call would never get a hangup event. This changes it so
that we always end a call by calling hangup, then do the cleanup
when the hangup event arrives, so the cleanup is the same whether
we hang up or the other side does.

* Some fixes for failing & hanging tests

* Add type for the call map

spec/unit/webrtc/groupCall.spec.ts

@@ -144,6 +144,10 @@ describe("Group Call", function () {
             } as unknown as RoomMember;
         });
 
+        afterEach(() => {
+            groupCall.leave();
+        });
+
         it.each(Object.values(GroupCallState).filter((v) => v !== GroupCallState.LocalCallFeedUninitialized))(
             "throws when initializing local call feed in %s state",
             async (state: GroupCallState) => {