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/inputmethod/AvailableVirtualKeyboardFragment.java

@@ -38,7 +38,6 @@ import com.android.internal.logging.nano.MetricsProto.MetricsEvent;
 import com.android.settings.R;
 import com.android.settings.SettingsPreferenceFragment;
 import com.android.settings.search.BaseSearchIndexProvider;
-import com.android.settings.search.Indexable;
 import com.android.settingslib.inputmethod.InputMethodAndSubtypeUtil;
 import com.android.settingslib.inputmethod.InputMethodPreference;
 import com.android.settingslib.inputmethod.InputMethodSettingValuesWrapper;
@@ -50,7 +49,7 @@ import java.util.List;
 
 @SearchIndexable
 public final class AvailableVirtualKeyboardFragment extends SettingsPreferenceFragment
-        implements InputMethodPreference.OnSavePreferenceListener, Indexable {
+        implements InputMethodPreference.OnSavePreferenceListener {
 
     private final ArrayList<InputMethodPreference> mInputMethodPreferenceList = new ArrayList<>();
     private InputMethodSettingValuesWrapper mInputMethodSettingValues;