WP.org Base Theme: Register navigation JS for use in child themes

[ryelle]

As of r6068, the navigation.js file has been commented out of the wporg parent theme, which means the child themes need to re-enqueue it from scratch (and if it's changed, the versions need to be bumped across all instances).

Instead, we could use wp_register_script in the parent theme to set up the file & information, and let child themes opt in to using it with wp_enqueue_script( 'wporg-navigation' ).

Example of a child theme re-enqueuing the file: https://meta.trac.wordpress.org/browser/sites/trunk/wordpress.org/public_html/wp-content/themes/pub/wporg-main/functions.php#L121