Add support for ACI safety numbers behind a feature flag

ts/util/isSafetyNumberNotAvailable.ts

@@ -0,0 +1,19 @@
+// Copyright 2023 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import type { ConversationType } from '../state/ducks/conversations';
+
+export const isSafetyNumberNotAvailable = (
+  contact?: ConversationType
+): boolean => {
+  // We have a contact
+  if (!contact) {
+    return true;
+  }
+  // They have a uuid
+  if (!contact.uuid) {
+    return true;
+  }
+  // The uuid is not PNI
+  return contact.pni === contact.uuid;
+};