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/users/UserSettings.java

@@ -96,7 +96,7 @@ public class UserSettings extends SettingsPreferenceFragment
         implements Preference.OnPreferenceClickListener, View.OnClickListener,
         MultiUserSwitchBarController.OnMultiUserSwitchChangedListener,
         DialogInterface.OnDismissListener,
-        EditUserInfoController.OnContentChangedCallback, Indexable {
+        EditUserInfoController.OnContentChangedCallback {
 
     private static final String TAG = "UserSettings";