Widgets: Trigger jQuery events for widget updates.
* `widget-added` when a widget is added to a sidebar
* `widget-updated` when a widget is updated
A jQuery object of the widget is passed along to the event handler. Same events are used in the Widget Customizer, see [27909].

fixes #19675.
Built from https://develop.svn.wordpress.org/trunk@27969


git-svn-id: http://core.svn.wordpress.org/trunk@27799 1a063a9b-81f0-0310-95a4-ce76da25c4cd