docs(router): filter the event to subscribe (#37027)

The current code will not work as the `e` will be an event,
If we try to access e.id and e.url it will throw an exception, the correct way is to use map or filter down to specific events

PR Close #37027

packages/router/src/events.ts

@@ -30,8 +30,8 @@ export type NavigationTrigger = 'imperative'|'popstate'|'hashchange';
  * class MyService {
  *   constructor(public router: Router, logger: Logger) {
  *     router.events.pipe(
- *       filter(e => e instanceof RouterEvent)
- *     ).subscribe(e => {
+ *        filter((e: Event): e is RouterEvent => e instanceof RouterEvent)
+ *     ).subscribe((e: RouterEvent) => {
  *       logger.log(e.id, e.url);
  *     });
  *   }