Cleanup how we setup the CallKit provider and have it be used for outgoing calls as well (#2967)

- tear down ElementCall screens when ending the call from the CXCallController
- make the call UI available in the task manager and lock screen
- Fix broken hang up widget message format

ElementX/Sources/Application/AppCoordinator.swift

@@ -149,10 +149,10 @@ class AppCoordinator: AppCoordinatorProtocol, AuthenticationFlowCoordinatorDeleg
             .receive(on: DispatchQueue.main)
             .sink { [weak self] action in
                 switch action {
-                case .answerCall(let roomID):
+                case .startCall(let roomID):
                     self?.handleAppRoute(.call(roomID: roomID))
-                case .declineCall:
-                    break
+                case .endCall:
+                    break // Handled internally in the UserSessionFlowCoordinator
                 }
             }
             .store(in: &cancellables)