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/tts/TtsEnginePreferenceFragment.java

@@ -26,8 +26,8 @@ import java.util.List;
 import androidx.preference.PreferenceCategory;
 
 @SearchIndexable
-public class TtsEnginePreferenceFragment extends SettingsPreferenceFragment //implements
-        implements RadioButtonGroupState, Indexable {
+public class TtsEnginePreferenceFragment extends SettingsPreferenceFragment
+        implements RadioButtonGroupState {
     private static final String TAG = "TtsEnginePrefFragment";
 
     private static final int VOICE_DATA_INTEGRITY_CHECK = 1977;