Programmatically embed a node or entity edit form in Drupal 8

node_edit_form_d8.php

// Without the use of D.I.
$form = \Drupal::service('entity.manager')
  ->getFormObject('node', 'default')
  ->setEntity($node);
$build[] = \Drupal::formBuilder()->getForm($form);

// Within a class using D.I.
class someClass {
  public function __construct(EntityManagerInterface $entityManager) {
    $this->entityManager = $entityManager;
  }

  public static function create(ContainerInterface $container) {
    return new static(
      $container->get('entity.manager')
    );
  }

  public function someFunction() {
    $build = array();
    $form = $this->entityManager
      ->getFormObject('node', 'default')
      ->setEntity($node);
    $build[] = \Drupal::formBuilder()->getForm($form);

    return $build;
  }
}