- Better structure, simpler "view" registration, better extensibility. - Better inline documentation. - Don't show a placeholder for pasted link until we know the link is "embeddable'. And many more improvements. Props iseulde. See #31412. Built from https://develop.svn.wordpress.org/trunk@31546 git-svn-id: http://core.svn.wordpress.org/trunk@31527 1a063a9b-81f0-0310-95a4-ce76da25c4cd