Design review updates for Taskbar Pinning

Changes:

- icon allignment animation for taskbar diviver view
- taskbar divider background color according to spec.

Test: Manual
Bug: 265170176
Flag: ENABLE_TASKBAR_PINNING
Change-Id: Ief45e48f4fc9f9b4cc30124c4c93cd3c5a880a33

quickstep/src/com/android/launcher3/taskbar/TaskbarView.java

@@ -514,6 +514,14 @@ public class TaskbarView extends FrameLayout implements FolderIcon.FolderIconPar
         return mAllAppsButton;
     }
 
+    /**
+     * Returns the taskbar divider in the taskbar.
+     */
+    @Nullable
+    public View getTaskbarDividerView() {
+        return mTaskbarDivider;
+    }
+
     /**
      * Returns the QSB in the taskbar.
      */