TinyMCE: fix the 'editimage' plugin for touch devices. Better attempt to hide the onscreen keyboard when the media modal opens and TinyMCE is in focus. See #28595, #29166

Built from https://develop.svn.wordpress.org/trunk@29471


git-svn-id: http://core.svn.wordpress.org/trunk@29249 1a063a9b-81f0-0310-95a4-ce76da25c4cd