feat(router): better warning message when a router outlet has not been instantiated (#30246)

It is confusing when routes are successfully activated but a component
is not present on a page, with this message it's more clear.

PR Close #30246

packages/router/src/operators/activate_routes.ts

@@ -6,6 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
+import {isDevMode} from '@angular/core';
 import {MonoTypeOperatorFunction} from 'rxjs';
 import {map} from 'rxjs/operators';
 
@@ -185,6 +186,10 @@ export class ActivateRoutes {
             // Activate the outlet when it has already been instantiated
             // Otherwise it will get activated from its `ngOnInit` when instantiated
             context.outlet.activateWith(future, cmpFactoryResolver);
+          } else if (isDevMode() && console && console.warn) {
+            console.warn(
+                `A router outlet has not been instantiated during routes activation. URL Segment: '${
+                    future.snapshot._urlSegment}'`);
           }
 
           this.activateChildRoutes(futureNode, null, context.children);