Update preference screen title.

- Add missing title to preference screen xml so that they will be used to
set the activity title when the fragment is launched.
- Also updated some incorrect preference screen titles.
- Overrides getTitle() in preference fragments that do not use the
preference screen xml.

Bug: 64564191
Test: blaze-bin/screenshots/android/i18nscreenshots/i18nscreenshots
Change-Id: Id72d5ddf18f0962bc484de8bbd847a2e55d6371e

src/com/android/settings/development/featureflags/FeatureFlagsDashboard.java

@@ -42,7 +42,7 @@ public class FeatureFlagsDashboard extends DashboardFragment {
 
     @Override
     protected int getPreferenceScreenResId() {
-        return R.xml.placeholder_prefs;
+        return R.xml.feature_flags_settings;
     }
 
     @Override