Improve shortcode support for link fields

[Code Muffin]

Using a shortcode in a link field currently prepends http:// to the field. They still render on the frontend, but this makes them functionally unusable because the resulting href is always prepended by that http://.

This is due to the JS function correctURL (in ​wp-includes/js/wplink.js), which adds it if the URL does not start with http:, https:, ? # or /.

I suggest adding [ to that list of allowed characters, so shortcodes can be used too.