feat(core): introduce fixture.whenRenderingDone for testing (#16732)

packages/core/testing/src/component_fixture.ts

@@ -160,6 +160,14 @@ export class ComponentFixture<T> {
     }
   }
 
+  /**
+   * Get a promise that resolves when the ui state is stable following animations.
+   */
+  whenRenderingDone(): Promise<any> {
+    // this is temporary until this is functional
+    return this.whenStable();
+  }
+
   /**
    * Trigger component destruction.
    */