Add a few pages to search index.

- Data saver
- A few special permission access pages
   - Picture-in-picture
   - Premium sms
   - do not disturb access
- And a unrelated cleanup: move EmptyTextFragment from
  notification/ to widget/

Bug: 70720645
Test: robotests
Change-Id: I6a87f712bf81f9fd32fa9a3826fba851ca748409

src/com/android/settings/applications/specialaccess/DataSaverController.java

@@ -31,7 +31,7 @@ public class DataSaverController extends BasePreferenceController {
     @AvailabilityStatus
     public int getAvailabilityStatus() {
         return mContext.getResources().getBoolean(R.bool.config_show_data_saver)
-                ? AVAILABLE
+                ? AVAILABLE_UNSEARCHABLE
                 : UNSUPPORTED_ON_DEVICE;
     }
 }