Sets the email $_POST value so WC will prefill the "email" field in the My Account registration form

wc-my-account-prefill-email.php

<?php
// get the email param if it's set so the registration form can use it
function sv_get_account_email_param() {
	$_POST['email'] = isset( $_GET['email'] ) ? urldecode( $_GET['email'] ) : false;
}
add_action( 'woocommerce_register_form_start', 'sv_get_account_email_param' );