Builds an entity form.
This is the entity form builder which is invoked via drupal_build_form() to retrieve the form.
array $form: A nested array form elements comprising the form.
array $form_state: An associative array containing the current state of the form.
string $entity_type: The type of the entity being edited.
\Drupal\Core\Entity\EntityInterface $entity: The entity being edited.
array The array containing the complete form.
public function build(array $form, array &$form_state, EntityInterface $entity);