fix(service-worker): listen for messages on the right event source (#19954)

Currently, the SwUpdate service doesn't receive messages from the SW.
This is because it attempts to subscribe to the 'message' event on
ServiceWorkerRegistration, when really messages are emitted by the
ServiceWorkerContainer.

This change moves to listening on ServiceWorkerContainer and changes
the mocks to reflect the way the browser actually works.

PR Close #19954

packages/service-worker/test/integration_spec.ts

@@ -85,7 +85,7 @@ export function main() {
       driver = new Driver(scope, scope, new CacheDatabase(scope, scope));
 
       scope.clients.add('default');
-      scope.clients.getMock('default') !.queue.subscribe(msg => { reg.sendMessage(msg); });
+      scope.clients.getMock('default') !.queue.subscribe(msg => { mock.sendMessage(msg); });
 
       mock.messages.subscribe(msg => { scope.handleMessage(msg, 'default'); });