In Drupal 7, I could use hook_admin_paths to decide if a page used the main or admin theme. This has changed in Drupal 8. This option is now set in a route definition. Existing routes, like node.add, can be altered. However, looking in node.routing.yml, under node.add, I do not see
_admin_route: TRUE, which I intended to alter to
What do I need to alter, and how, so that adding and editing nodes is done using the main theme?