Set height/width on responsive images

theme.php

<?php

/**
 * Implements hook_preprocess_responsive_image_formatter().
 */
function theme_preprocess_responsive_image_formatter(&$variables) {
  $item = $variables['item'];
  $height = $item->get('height')->getValue();
  $width = $item->get('width')->getValue();
  if (!$variables['responsive_image']['#width']) {
    $variables['responsive_image']['#width'] = $width;
  }
  if (!$variables['responsive_image']['#height']) {
    $variables['responsive_image']['#height'] = $height;
  }
}