Misc tweaks to Indexable usage and tests.

- Make SettingsPreferenceFragment implement Indexable directly
- Add existing fragments that are SettingsPrefFragment but not Indexable
  to grandfather list.
- Fix "font size" fragment so it shows up in search properly.
- Remove duplicates for "lock screen display", "Screen saver".

Bug: 70720645
Test: robotests
Change-Id: I44ce0cac0fdf5e882b315861bb4bebc45dbe01e6

src/com/android/settings/slices/SliceBuilderUtils.java

@@ -32,7 +32,6 @@ import android.text.TextUtils;
 import android.util.Log;
 import android.util.Pair;
 
-import com.android.internal.annotations.VisibleForTesting;
 import com.android.internal.logging.nano.MetricsProto.MetricsEvent;
 import com.android.settings.R;
 import com.android.settings.SettingsActivity;
@@ -230,8 +229,7 @@ public class SliceBuilderUtils {
         return searchDestination;
     }
 
-    @VisibleForTesting
-    static Intent getContentIntent(Context context, SliceData sliceData) {
+    public static Intent getContentIntent(Context context, SliceData sliceData) {
         final Uri contentUri = new Uri.Builder().appendPath(sliceData.getKey()).build();
         final Intent intent = buildSearchResultPageIntent(context,
                 sliceData.getFragmentClassName(), sliceData.getKey(),