refactor(router): cleanup to navigation stream for readability and documentation (#25740)

* Pull out `activateRoutes` into new operator
* Add `asyncTap` operator
* Use `asyncTap` operator for router hooks and remove corresponding abstracted operators
* Clean up formatting
* Minor performance improvements

PR Close #25740

packages/router/src/operators/check_guards.ts

@@ -16,7 +16,7 @@ export function checkGuards(): MonoTypeOperatorFunction<NavigationTransition> {
 
     return source.pipe(mergeMap(t => {
       if (!t.preActivation) {
-        throw 'Initialized PreActivation required to check guards';
+        throw new Error('PreActivation required to check guards');
       }
       return t.preActivation.checkGuards().pipe(map(guardsResult => ({...t, guardsResult})));
     }));