Fixing tab order on Drupal content edit forms for keyboard accessibility

Documentation: https://www.drupal.org/docs/drupal-apis/javascript-api/accessibility-tools-for-javascript-in-drupal-8

Specifically: https://www.drupal.org/docs/drupal-apis/javascript-api/accessibility-tools-for-javascript-in-drupal-8#tabbing

Announcement: New accessibility feature: Drupal.tabbingManager | Drupal.org