Replace generateKeyed$ with a redesigned generateItems operator

And use it to clean up a number of code smells, fix some reactivity bugs, and avoid some resource leaks.

src/state/ScreenShare.ts

@@ -4,7 +4,7 @@ Copyright 2025 New Vector Ltd.
 SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
-import { of, type Observable } from "rxjs";
+import { of } from "rxjs";
 import {
   type LocalParticipant,
   type RemoteParticipant,
@@ -13,7 +13,6 @@ import {
 
 import { type ObservableScope } from "./ObservableScope.ts";
 import { ScreenShareViewModel } from "./MediaViewModel.ts";
-import type { RoomMember } from "matrix-js-sdk";
 import type { EncryptionSystem } from "../e2ee/sharedKeyManagement.ts";
 import type { Behavior } from "./Behavior.ts";
 
@@ -28,24 +27,26 @@ export class ScreenShare {
   public constructor(
     private readonly scope: ObservableScope,
     id: string,
-    member: RoomMember,
+    userId: string,
     participant: LocalParticipant | RemoteParticipant,
     encryptionSystem: EncryptionSystem,
-    livekitRoom: LivekitRoom,
-    focusUrl: string,
+    livekitRoom$: Behavior<LivekitRoom | undefined>,
+    focusUrl$: Behavior<string | undefined>,
     pretendToBeDisconnected$: Behavior<boolean>,
-    displayName$: Observable<string>,
+    displayName$: Behavior<string>,
+    mxcAvatarUrl$: Behavior<string | undefined>,
   ) {
     this.vm = new ScreenShareViewModel(
       this.scope,
       id,
-      member,
+      userId,
       of(participant),
       encryptionSystem,
-      livekitRoom,
-      focusUrl,
+      livekitRoom$,
+      focusUrl$,
       pretendToBeDisconnected$,
-      this.scope.behavior(displayName$),
+      displayName$,
+      mxcAvatarUrl$,
       participant.isLocal,
     );
   }