Make screen sharing work more like speaking marbles in tests

This approach is more flexible in that it allows even the local participant to share their screen in CallViewModel tests, and more rigorous in that it ensures that application code is reacting specifically to track publications.

src/state/CallViewModel/CallViewModelTestUtils.ts

@@ -15,7 +15,7 @@ import {
   type Room as LivekitRoom,
 } from "livekit-client";
 import { SyncState } from "matrix-js-sdk/lib/sync";
-import { BehaviorSubject, type Observable, map, of } from "rxjs";
+import { BehaviorSubject, combineLatest, map, of } from "rxjs";
 import { onTestFinished, vi } from "vitest";
 import { ClientEvent, type RoomMember, type MatrixClient } from "matrix-js-sdk";
 import EventEmitter from "events";
@@ -68,7 +68,8 @@ export interface CallViewModelInputs {
   rtcMembers$: Behavior<Partial<CallMembership>[]>;
   roomMembers: RoomMember[];
   livekitConnectionState$: Behavior<ConnectionState>;
-  speaking: Map<Participant, Observable<boolean>>;
+  speaking: Map<Participant, Behavior<boolean>>;
+  sharingScreen: Map<Participant, Behavior<boolean>>;
   mediaDevices: MediaDevices;
   initialSyncState: SyncState;
   windowSize$: Behavior<{ width: number; height: number }>;
@@ -94,6 +95,7 @@ export function withCallViewModel(mode: MatrixRTCMode) {
         ConnectionState.Connected,
       ),
       speaking = new Map(),
+      sharingScreen = new Map(),
       mediaDevices = mockMediaDevices({}),
       initialSyncState = SyncState.Syncing,
       windowSize$ = constant({ width: 1000, height: 800 }),
@@ -154,13 +156,19 @@ export function withCallViewModel(mode: MatrixRTCMode) {
     const eventsSpy = vi
       .spyOn(ComponentsCore, "observeParticipantEvents")
       .mockImplementation((p, ...eventTypes) => {
-        if (eventTypes.includes(ParticipantEvent.IsSpeakingChanged)) {
-          return (speaking.get(p) ?? of(false)).pipe(
-            map((s): Participant => ({ ...p, isSpeaking: s }) as Participant),
-          );
-        } else {
-          return of(p);
-        }
+        return combineLatest([
+          (eventTypes.includes(ParticipantEvent.IsSpeakingChanged) &&
+            speaking.get(p)) ||
+            constant(false),
+          (eventTypes.includes(ParticipantEvent.TrackPublished) &&
+            sharingScreen.get(p)) ||
+            constant(false),
+        ]).pipe(
+          map(
+            ([isSpeaking, isScreenShareEnabled]) =>
+              ({ ...p, isSpeaking, isScreenShareEnabled }) as Participant,
+          ),
+        );
       });
 
     const roomEventSelectorSpy = vi