Constructs a ValidReferenceConstraintValidator object.
\Drupal\Core\Entity\EntityReferenceSelection\SelectionPluginManagerInterface $selection_manager: The selection plugin manager.
\Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager: The entity type manager.
public function __construct(SelectionPluginManagerInterface $selection_manager, EntityTypeManagerInterface $entity_type_manager) {
$this->selectionManager = $selection_manager;
$this->entityTypeManager = $entity_type_manager;
}