When settting a featured image, move the currently selected image to the...

When settting a featured image, move the currently selected image to the beginning of the library if it doesn't exist within the attachments loaded so far.

Props koopersmith
fixes #22494


git-svn-id: https://core.svn.wordpress.org/trunk@22993 1a063a9b-81f0-0310-95a4-ce76da25c4cd