introduce RecyclerCollectionEventsController#scrollBy method

Summary: Adding `public void requestScrollBy(int dx, int dy)` to `RecyclerCollectionEventsController` class

Reviewed By: mihaelao

Differential Revision: D15308395

fbshipit-source-id: db1356ca9dea7feb3a630532525f0c76f8699a56

litho-sections-widget/src/main/java/com/facebook/litho/sections/widget/RecyclerCollectionEventsController.java

@@ -112,6 +112,19 @@ public void requestScrollToPositionWithSnap(
     requestScrollToPositionInner(true, target, target, smoothScroller);
   }
 
+  /**
+   * Send the {@link RecyclerCollectionComponent} a request to scroll the content by the given
+   * margins.
+   */
+  public void requestScrollBy(int dx, int dy) {
+    final RecyclerView recyclerView = getRecyclerView();
+    if (recyclerView == null) {
+      return;
+    }
+
+    recyclerView.scrollBy(dx, dy);
+  }
+
   /**
    * @param animated whether the scroll will happen with animation.
    * @param defaultTarget target to use as fallback.