Show title, album, and artist info for audio files displayed in `WP_Customize_Upload_Control()`.

See #21483.


git-svn-id: https://develop.svn.wordpress.org/trunk@30737 602fd350-edb4-49c9-b593-d223f7449a82
Add some inline JS docs for Customizer.

See #30469.


git-svn-id: https://develop.svn.wordpress.org/trunk@30738 602fd350-edb4-49c9-b593-d223f7449a82