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.
Valere