* Edit shortcuts show initially for a moment and then fade away so as to not get in the way of the preview.
* Visibility of edit shortcuts is toggled by clicking/touching anywhere inert in the document.
* Implements UI for mobile and touch devices which do not support shift-click.
* Adds `editShortcutVisibility` state.
* Adds new methods to `wp.customize.selectiveRefresh.Partial` for managing edit shortcuts.
Incorporates aspects of the Customize Direct Manipulation feature plugin.
Props sirbrillig, mattwiebe, celloexpressions, melchoyce, westonruter, afercia.
Fixes#27403.
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git-svn-id: http://core.svn.wordpress.org/trunk@38910 1a063a9b-81f0-0310-95a4-ce76da25c4cd
