fix(router): export navigation extras

tools/public_api_guard/router/index.d.ts

@@ -79,6 +79,13 @@ export declare class NavigationError {
     toString(): string;
 }
 
+/** @experimental */
+export interface NavigationExtras {
+    fragment?: string;
+    queryParams?: Params;
+    relativeTo?: ActivatedRoute;
+}
+
 /** @stable */
 export declare class NavigationStart {
     id: number;