[ps] Add helper function to scroll a recycler view to bottom and `resetAndScrollToPrivateSpace`.

Bug: 309522136
Test: manual
Flag: ACONFIG com.google.android.apps.nexuslauncher.inject_private_space_tile DEVELOPMENT
Change-Id: I96a1eed97dd1e4626ddc5ad42c029d94eb174f00
diff --git a/src/com/android/launcher3/FastScrollRecyclerView.java b/src/com/android/launcher3/FastScrollRecyclerView.java
index 67ed55d..01e65ae 100644
--- a/src/com/android/launcher3/FastScrollRecyclerView.java
+++ b/src/com/android/launcher3/FastScrollRecyclerView.java
@@ -192,4 +192,14 @@
         }
         scrollToPosition(0);
     }
+
+    /**
+     * Scrolls this recycler view to the bottom.
+     */
+    public void scrollToBottom() {
+        if (mScrollbar != null) {
+            mScrollbar.reattachThumbToScroll();
+        }
+        smoothScrollToPosition(getAdapter().getItemCount() - 1);
+    }
 }