Customizer: When widget reorder button is actioned, transfer focus to the first Move control within the section.

fixes #28891.
Built from https://develop.svn.wordpress.org/trunk@29242


git-svn-id: http://core.svn.wordpress.org/trunk@29026 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Customizer: Remove "Add a Widget" button from tab order when reordering widgets.

fixes #28890.
Built from https://develop.svn.wordpress.org/trunk@29243


git-svn-id: http://core.svn.wordpress.org/trunk@29027 1a063a9b-81f0-0310-95a4-ce76da25c4cd