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/datausage/DataUsageSummary.java

@@ -51,8 +51,7 @@ import androidx.preference.PreferenceScreen;
  * Settings preference fragment that displays data usage summary.
  */
 @SearchIndexable(forTarget = SearchIndexable.ALL & ~SearchIndexable.ARC)
-public class DataUsageSummary extends DataUsageBaseFragment implements Indexable,
-        DataUsageEditController {
+public class DataUsageSummary extends DataUsageBaseFragment implements DataUsageEditController {
 
     private static final String TAG = "DataUsageSummary";
 
@@ -379,6 +378,9 @@ public class DataUsageSummary extends DataUsageBaseFragment implements Indexable
                 // This title is named Wifi, and will confuse users.
                 keys.add(KEY_WIFI_USAGE_TITLE);
 
+                // Duplicate entry for "Data saver"
+                keys.add(KEY_RESTRICT_BACKGROUND);
+
                 return keys;
             }
         };