Move the state layer onto the host bridge

MuteStates, CallViewModel and LocalMember reached the host through the
widget global. None of them are React components, so they take the bridge
as an explicit parameter: a constructor argument for MuteStates, a field
on CallViewModelOptions, and one on createLocalMembership$'s props.

src/state no longer refers to the widget API.

The conditionals around it mostly disappear: nullHostBridge's observables
are NEVER, so there is nothing to guard, and a request carries its own
reply rather than needing the transport and the original event.

CallViewModelWidget.test.ts drove hangup by emitting on the mocked
widget's action emitter, so it now injects a bridge instead, and checks
that the request is acknowledged.

src/state/CallViewModel/CallViewModel.ts

@@ -48,7 +48,6 @@ import {
   type RTCCallIntent,
   type RTCNotificationType,
 } from "matrix-js-sdk/lib/matrixrtc";
-import { type IWidgetApiRequest } from "matrix-widget-api";
 import { type CallMembershipIdentityParts } from "matrix-js-sdk/lib/matrixrtc/EncryptionManager";
 import { v4 as uuidv4 } from "uuid";
 import { type IMembershipManager } from "matrix-js-sdk/lib/matrixrtc/IMembershipManager";
@@ -89,7 +88,7 @@ import { MatrixKeyProvider } from "../../e2ee/matrixKeyProvider";
 import { type MuteStates } from "../MuteStates";
 import { HeaderStyle } from "../../UrlParams";
 import { type ProcessorState } from "../../livekit/TrackProcessorContext";
-import { ElementWidgetActions, widget } from "../../widget";
+import { type HostBridge, nullHostBridge } from "../../HostBridge";
 import {
   layoutShallowEquals,
   type Alignment,
@@ -173,6 +172,11 @@ import { type GridTileViewModel } from "../TileViewModel.ts";
 // callMembership -> rtcMembership
 export interface CallViewModelOptions {
   encryptionSystem: EncryptionSystem;
+  /**
+   * The application hosting Element Call, which can ask it to hang up and wants
+   * to know when the user joins or leaves. Defaults to no host.
+   */
+  hostBridge?: HostBridge;
   /**
    * Whether the app hosting Element Call controls the audio output devices,
    * rather than the browser. Defaults to false.
@@ -457,6 +461,7 @@ export function createCallViewModel$(
   // Defaults match what the URL parameters resolve to outside of widget mode,
   // so that callers which don't care (chiefly tests) behave as they always have.
   const {
+    hostBridge = nullHostBridge,
     controlledAudioDevices = false,
     header = HeaderStyle.Standard,
     showControls = true,
@@ -632,6 +637,7 @@ export function createCallViewModel$(
     localTransport$,
     roomId: matrixRoom.roomId,
     hideScreensharing,
+    hostBridge,
     logger: logger.getChild(`[${Date.now()}]`),
   });
 
@@ -923,24 +929,16 @@ export function createCallViewModel$(
 
   const userHangup$ = new Subject<void>();
 
-  const widgetHangup$ =
-    widget === null
-      ? NEVER
-      : (
-          fromEvent(
-            widget.lazyActions,
-            ElementWidgetActions.HangupCall,
-          ) as Observable<CustomEvent<IWidgetApiRequest>>
-        ).pipe(
-          tap((ev) => {
-            widget!.api.transport.reply(ev.detail, {});
-          }),
-        );
+  const hostHangup$ = hostBridge.hangUp$.pipe(
+    tap((request) => {
+      request.reply();
+    }),
+  );
 
   const leave$: Observable<"user" | "timeout" | "decline" | "allOthersLeft"> =
     merge(
       autoLeave$,
-      merge(userHangup$, widgetHangup$).pipe(map(() => "user" as const)),
+      merge(userHangup$, hostHangup$).pipe(map(() => "user" as const)),
     ).pipe(scope.share);
 
   const spotlightSpeaker$ = scope.behavior<UserMediaViewModel | undefined>(