Conditionally require Drupal 8 fields and subfields in an address webform

ConditionallyRequiredWebformFields.php

<?php

/**
 * Implements hook_form_FORM_ID_alter().
 */
function mymodule_form_webform_submission_registration_form_alter(array &$form, FormStateInterface $form_state) {
  // Show 'Country' as first field.
  $form['elements']['personal_information']['address']['#country__weight'] = -2;
  // Show 'State' next, but conditionally.
  $form['elements']['personal_information']['address']['#state_province__weight'] = -1;
  $form['elements']['personal_information']['address']['#city__weight'] = 0;
  // If user selects 'United States' for Country, State and City fields are required.
  $form['elements']['personal_information']['address']['#state_province__states'] = [
    'required' => [
      ':input[name="address[country]"]' => ['value' => 'United States']
    ],
  ];
  $form['elements']['personal_information']['address']['#city__states'] = [
    'required' => [
      ':input[name="address[country]"]' => ['value' => 'United States']
    ],
  ];
  $form['#attached']['library'][] = 'mymodule/registration_form';
  // Add custom validation to ensure City and State are filled out if Country is 'United States'.
  $form['#validate'][] = '_mymodule_webform_submission_registration_form_validate';
  return $form;
}

/**
 * Validates submission values in the FORM_ID() form.
 */
function _mymodule_webform_submission_registration_form_validate($form, FormStateInterface $form_state) {
  $values = $form_state->getValues();
  if (!empty($values['address']['country'] && $values['address']['country'] === 'United States')) {
    if (empty($values['address']['city'])) {
      $form_state->setErrorByName("address[city]", t('City is a required field for U.S. locations'));
    }
    if (empty($values['address']['state_province'])) {
      $form_state->setErrorByName("address[state_province]", t('State is a required field for U.S. locations'));
    }
  }
}