Drupal8: Clear Drupal caches after enabling extension

After enabling an extension (e.g. KAM) new menu callbacks are registered in civicrm_menu but not in Drupal, resulting in a 404 Not Found error when visiting pages provided by the extension. Manually clearing the Drupal cache fixes this.

I suspect that Drupal caches are not being adequately cleared by CiviCRM, which is probably a low-level problem affecting more than just this.