Media: Add awareness to Attachment Display Settings that audio and video can be embedded.

Also:
 * Add file length metadata to Attachment Details.
 * Round the kb/s bitrate on post.php.

fixes #24449.



git-svn-id: https://core.svn.wordpress.org/trunk@24777 1a063a9b-81f0-0310-95a4-ce76da25c4cd