drupal-34165856: alter local.module to properly check whether a JS file is local or not.

https://www.drupal.org/project/drupal/issues/3416586

Use existing UrlHelper methods to determine whether a JS file is local or not, rather than depending on the presence/lack of a colon (":"). This patch prevents locale.module from incorrectly throwing exceptions on local JS files that contain a colon in the path.