Media: Move sidebar from the frame view to the attachment browser view....

Media: Move sidebar from the frame view to the attachment browser view. Prevents juggling sidebar visibility state, and makes managing sidebar contents more reasonable. see #21390.


git-svn-id: https://core.svn.wordpress.org/trunk@22809 1a063a9b-81f0-0310-95a4-ce76da25c4cd