NodeController::add() method is deprecated

As the official entity API documentation recommends entity form routes should be defined through the _entity_form directive instead through the _controller one.

For the route node.add we had a controller which was doing nothing else but forward the call to the entity form builder, which is being done automatically by the _entity_form directive.

Therefore the route node.add is now defined through _entity_form and the controller \Drupal\node\Controller\NodeController::add() is now deprecated and scheduled for removal in Drupal 9.