Fix the preview should keep the same layer after font or display size change.

Bug: 259213786
Test: make RunSettingsRoboTests ROBOTEST_FILTER=TextReadingPreviewPreferenceTest
Change-Id: Ifc0047e47806662174712bb8628193bee906b384

src/com/android/settings/accessibility/TextReadingPreviewController.java

@@ -133,6 +133,14 @@ class TextReadingPreviewController extends BasePreferenceController implements
         postCommitDelayed(CHANGE_BY_SEEKBAR_DELAY_MS);
     }
 
+    void setCurrentItem(int index) {
+        mPreviewPreference.setCurrentItem(index);
+    }
+
+    int getCurrentItem() {
+        return mPreviewPreference.getCurrentItem();
+    }
+
     /**
      * The entry point is used for logging.
      *