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

See #27016.



git-svn-id: https://develop.svn.wordpress.org/trunk@27642 602fd350-edb4-49c9-b593-d223f7449a82
Fixes for `jshint`


git-svn-id: https://develop.svn.wordpress.org/trunk@27643 602fd350-edb4-49c9-b593-d223f7449a82