Add some JSDoc annotations to `media-models.js` to disambiguate instance properties and static class properties/methods in the base media Models.

See #26870.


Built from https://develop.svn.wordpress.org/trunk@27031


git-svn-id: http://core.svn.wordpress.org/trunk@26907 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Add some inline docs to methods in `media-models.js` - particularly around `@param` and `@returns`.

See #26870.


Built from https://develop.svn.wordpress.org/trunk@27032


git-svn-id: http://core.svn.wordpress.org/trunk@26908 1a063a9b-81f0-0310-95a4-ce76da25c4cd