Adds `wp.shortcode`, a set of methods used for parsing shortcodes out of content. Also adds a default set of shortcode properties to `wp.mce.view`.
fixes#21996, see #21812, #21813, #21815.
git-svn-id: https://develop.svn.wordpress.org/trunk@22004 602fd350-edb4-49c9-b593-d223f7449a82
Daryl Koopersmith