Returns response for the user autocompletion with the anonymous user.
\Symfony\Component\HttpFoundation\Request $request: The current request object containing the search string.
\Symfony\Component\HttpFoundation\JsonResponse A JSON response containing the autocomplete suggestions for existing users.
\Drupal\user\UserAutocomplete::autocompleteUser()
public function autocompleteUserAnonymous(Request $request) {
return $this
->autocompleteUser($request, TRUE);
}