`audio`, `video`, and `playlist` shortcodes:

* Convert all instances of variable variables to array properties
* Eradicate use of `extract()`
* Rename `$atts` to `$html_atts` where collision with new `$atts` (shortcode atts holder) var might occur

See #22400, #27881.



git-svn-id: https://develop.svn.wordpress.org/trunk@28342 602fd350-edb4-49c9-b593-d223f7449a82