Option to make country an autocomplete textfield

Just going to add this here for anyone landing here wanting to do this for all address_country form elements by default without having to write/configure custom FormElements/FormWidgets.

/**
 * Implements hook_element_info_alter()
 */
function mymodule_element_info_alter(array &$info) {
  if (isset($info['address_country'])) {
    // Add a process callback (after the defaults) for address_country form elements
    $info['address_country']['#process'][] = 'mymodule_process_address_country';
  }
}

/**
 * Process callback for all address_country form elements
 *
 * @param array $element
 * @param \Drupal\Core\Form\FormStateInterface $form_state
 *
 * @return array
 */
function mymodule_process_address_country(array &$element, FormStateInterface $form_state) {
  $element['country_code']['#type'] = 'select2';
  return $element;
}

This will change the address_country element everywhere it is used on the site(even within the full address widget). If you want to be able to pick and choose where select2 is used, use one of the widget examples above!

Cheers!