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/security/screenlock/LockScreenPreferenceController.java

@@ -54,11 +54,11 @@ public class LockScreenPreferenceController extends BasePreferenceController imp
     public int getAvailabilityStatus() {
         if (!mLockPatternUtils.isSecure(MY_USER_ID)) {
             return mLockPatternUtils.isLockScreenDisabled(MY_USER_ID)
-                    ? DISABLED_FOR_USER : AVAILABLE;
+                    ? DISABLED_FOR_USER : AVAILABLE_UNSEARCHABLE;
         } else {
             return mLockPatternUtils.getKeyguardStoredPasswordQuality(MY_USER_ID)
                     == PASSWORD_QUALITY_UNSPECIFIED
-                    ? DISABLED_FOR_USER : AVAILABLE;
+                    ? DISABLED_FOR_USER : AVAILABLE_UNSEARCHABLE;
         }
     }