Flag guard the quarantined apps screen

Ensure the screen itself is flag-guarded, not just the entry point
in Developer Options.

Fixes: 311724167
Test: m -j
      flash, ensure feature is off, search for quarantined in Settings
      search, ensure no results
Change-Id: I4efaf1f7c6452d2ce6115f40fffa16963ee7c244

src/com/android/settings/development/quarantine/QuarantinedAppsScreenController.java

@@ -18,6 +18,7 @@ package com.android.settings.development.quarantine;
 
 import android.app.Application;
 import android.content.Context;
+import android.content.pm.Flags;
 import android.content.pm.PackageManager;
 import android.content.pm.SuspendDialogInfo;
 import android.os.UserHandle;
@@ -198,7 +199,7 @@ public class QuarantinedAppsScreenController extends BasePreferenceController im
 
     @Override
     public int getAvailabilityStatus() {
-        return AVAILABLE;
+        return Flags.quarantinedEnabled() ? AVAILABLE : CONDITIONALLY_UNAVAILABLE;
     }
 
     @Override