feat(router): allow guards to return UrlTree as well as boolean (#26521)

* Removed `andObservable` helper function in favor of inline implementation
* Flow `boolean | UrlTree` through guards check
* Add tests to verify behavior of `checkGuards` function flowing `UrlTree` properly

PR Close #26521

packages/router/test/helpers.ts

@@ -19,7 +19,7 @@ export class Logger {
   empty() { this.logs.length = 0; }
 }
 
-export function provideTokenLogger(token: string, returnValue = true) {
+export function provideTokenLogger(token: string, returnValue = true as boolean | UrlTree) {
   return {
     provide: token,
     useFactory: (logger: Logger) => () => (logger.add(token), returnValue),