Put grammatical gender developer option behind flag

Test: Automatic
Fixes: 312492402
Change-Id: I24476a69e149732fb8626c3253e06436c31eb7a0

src/com/android/settings/development/GrammaticalGenderPreferenceController.java

@@ -95,4 +95,9 @@ public class GrammaticalGenderPreferenceController extends DeveloperOptionsPrefe
         listPreference.setValue(mListValues[index]);
         listPreference.setSummary(mListSummaries[index]);
     }
+
+    @Override
+    public boolean isAvailable() {
+        return android.app.Flags.systemTermsOfAddressEnabled();
+    }
 }