Refactor GroupCall participant management

This refactoring brings a number of improvements to GroupCall, which I've unfortunately had to combine into a single commit due to coupling:

- Moves the expiration timestamp field on call membership state to be per-device
- Makes the participants of a group call visible without having to enter the call yourself
- Enables users to join group calls from multiple devices
- Identifies active speakers by their call feed, rather than just their user ID
- Plays nicely with clients that can be in multiple calls in a room at once
- Fixes a memory leak caused by the call retry loop never stopping
- Changes GroupCall to update its state synchronously, and write back to room state asynchronously
  - This was already sort of halfway being done, but now we'd be committing to it
  - Generally improves the robustness of the state machine
  - It means that group call joins will appear instant, in a sense

For many reasons, this is a breaking change.

spec/unit/webrtc/groupCallEventHandler.spec.ts

@@ -16,26 +16,21 @@ limitations under the License.
 
 import { mocked } from "jest-mock";
 
+import { ClientEvent } from "../../../src/client";
+import { RoomMember } from "../../../src/models/room-member";
+import { SyncState } from "../../../src/sync";
 import {
-    ClientEvent,
-    GroupCall,
     GroupCallIntent,
     GroupCallState,
     GroupCallType,
-    IContent,
-    MatrixEvent,
-    Room,
-    RoomState,
-} from "../../../src";
-import { SyncState } from "../../../src/sync";
-import { GroupCallTerminationReason } from "../../../src/webrtc/groupCall";
+    GroupCallTerminationReason,
+} from "../../../src/webrtc/groupCall";
+import { IContent, MatrixEvent } from "../../../src/models/event";
+import { Room } from "../../../src/models/room";
+import { RoomState } from "../../../src/models/room-state";
 import { GroupCallEventHandler, GroupCallEventHandlerEvent } from "../../../src/webrtc/groupCallEventHandler";
 import { flushPromises } from "../../test-utils/flushPromises";
-import {
-    makeMockGroupCallMemberStateEvent,
-    makeMockGroupCallStateEvent,
-    MockCallMatrixClient,
-} from "../../test-utils/webrtc";
+import { makeMockGroupCallStateEvent, MockCallMatrixClient } from "../../test-utils/webrtc";
 
 const FAKE_USER_ID = "@alice:test.dummy";
 const FAKE_DEVICE_ID = "AAAAAAA";
@@ -47,6 +42,7 @@ describe('Group Call Event Handler', function() {
     let groupCallEventHandler: GroupCallEventHandler;
     let mockClient: MockCallMatrixClient;
     let mockRoom: Room;
+    let mockMember: RoomMember;
 
     beforeEach(() => {
         mockClient = new MockCallMatrixClient(
@@ -54,13 +50,21 @@ describe('Group Call Event Handler', function() {
         );
         groupCallEventHandler = new GroupCallEventHandler(mockClient.typed());
 
+        mockMember = {
+            userId: FAKE_USER_ID,
+            membership: "join",
+        } as unknown as RoomMember;
+
         mockRoom = {
+            on: () => {},
+            off: () => {},
             roomId: FAKE_ROOM_ID,
             currentState: {
                 getStateEvents: jest.fn().mockReturnValue([makeMockGroupCallStateEvent(
                     FAKE_ROOM_ID, FAKE_GROUP_CALL_ID,
                 )]),
             },
+            getMember: (userId: string) => userId === FAKE_USER_ID ? mockMember : null,
         } as unknown as Room;
 
         (mockClient as any).getRoom = jest.fn().mockReturnValue(mockRoom);
@@ -211,27 +215,6 @@ describe('Group Call Event Handler', function() {
         );
     });
 
-    it("sends member events to group calls", async () => {
-        await groupCallEventHandler.start();
-
-        const mockGroupCall = {
-            onMemberStateChanged: jest.fn(),
-        };
-
-        groupCallEventHandler.groupCalls.set(FAKE_ROOM_ID, mockGroupCall as unknown as GroupCall);
-
-        const mockStateEvent = makeMockGroupCallMemberStateEvent(FAKE_ROOM_ID, FAKE_GROUP_CALL_ID);
-
-        mockClient.emitRoomState(
-            mockStateEvent,
-            {
-                roomId: FAKE_ROOM_ID,
-            } as unknown as RoomState,
-        );
-
-        expect(mockGroupCall.onMemberStateChanged).toHaveBeenCalledWith(mockStateEvent);
-    });
-
     describe("ignoring invalid group call state events", () => {
         let mockClientEmit: jest.Func;