Use fSelect for Hierarchy Select facets

<?php

add_action( 'wp_footer', function() {
?>
<link href="/wp-content/plugins/facetwp/assets/vendor/fSelect/fSelect.css" rel="stylesheet" type="text/css">
<script src="/wp-content/plugins/facetwp/assets/vendor/fSelect/fSelect.js"></script>
<script>
document.addEventListener('facetwp-loaded', function() {
    fUtil('.facetwp-hierarchy_select.is-disabled').addClass('fs-hidden');
    fUtil('.facetwp-hierarchy_select:not(.fs-hidden').fSelect();
});
</script>
<?php
}, 100 );