feat(router): throw a helpful error when misusing forRoot() from a lazy module. (#10996)

tools/public_api_guard/router/index.d.ts

@@ -239,6 +239,7 @@ export declare class RouterLinkWithHref implements OnChanges, OnDestroy {
 
 /** @stable */
 export declare class RouterModule {
+    constructor(guard: any);
     static forChild(routes: Routes): ModuleWithProviders;
     static forRoot(routes: Routes, config?: ExtraOptions): ModuleWithProviders;
 }