Add JSDoc blocks to `media-audiovideo.js`.

See #27016.


Built from https://develop.svn.wordpress.org/trunk@27642


git-svn-id: http://core.svn.wordpress.org/trunk@27485 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Fixes for `jshint`

Built from https://develop.svn.wordpress.org/trunk@27643


git-svn-id: http://core.svn.wordpress.org/trunk@27486 1a063a9b-81f0-0310-95a4-ce76da25c4cd