Presumably when not using Annotation you would do something like

    $form->add(array(
        'name' => 'entity_name',
        'type' => 'DoctrineORMModule\Form\Element\EntitySelect',
        'options' => array(
                'object_manager' => $entityManager,
        )
    ));

However when using Annotations to build a form you cannot set object_manager to an instance. So here I'm getting the AnnotationBuilder to do it for these types of Element.