Issue #3315187: Added options_select widget support.

jsonapi_reference.module

@@ -28,6 +28,7 @@ function jsonapi_reference_help($route_name, RouteMatchInterface $route_match) {
  */
 function jsonapi_reference_field_widget_info_alter(array &$info) {
   $info['string_textfield']['field_types'][] = 'typed_resource_object';
+  $info['options_select']['field_types'][] = 'typed_resource_object';
   $info['options_buttons']['field_types'][] = 'typed_resource_object';
 }