WooCommerce Checkout - Make the email field appear first

functions.php

<?php

// Minimum version WC 3.0
add_filter( 'woocommerce_checkout_fields', 'my_filter_woocommerce_checkout_fields');

function my_filter_woocommerce_checkout_fields($fields) {
  $fields['billing']['billing_email']['priority'] = 5;
  $fields['billing']['billing_email']['class'] = array( 'form-row-wide' );
  return $fields;
}