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/utils/test.ts

@@ -63,6 +63,7 @@ import { type MediaDevices } from "../state/MediaDevices";
 import { type Behavior, constant } from "../state/Behavior";
 import { ObservableScope } from "../state/ObservableScope";
 import { MuteStates } from "../state/MuteStates";
+import { nullHostBridge } from "../HostBridge";
 import {
   createLocalUserMedia,
   type LocalUserMediaViewModel,
@@ -577,10 +578,12 @@ export function mockMuteStates(
   joined$: Observable<boolean> = of(true),
 ): MuteStates {
   const observableScope = new ObservableScope();
-  return new MuteStates(observableScope, mockMediaDevices({}), {
-    audioEnabled: false,
-    videoEnabled: false,
-  });
+  return new MuteStates(
+    observableScope,
+    mockMediaDevices({}),
+    { audioEnabled: false, videoEnabled: false },
+    nullHostBridge,
+  );
 }
 
 export class MockConnection extends Connection {