Strongly type `Router.events.on` and `Router.events.off` (#26456)
This strongly types `Router.events.on` and `Router.events.off`. Previously the event type was `string` but now it's `'routeChangeStart' | 'beforeHistoryChange' | 'routeChangeComplete' | 'routeChangeError' | 'hashChangeStart' | 'hashChangeComplete'`
## Bug
- ~[ ] Related issues linked using `fixes #number`~
- [x] Integration tests added
Closes #25679
Closes #23753
Closes #15497