T97425 created two widgets but they're not exposed anywhere.

Since we don't have a public demo for mediawiki widgets, maybe we can use the API documentation examples for now as a place to provide an interactive test demo and example show case.

https://doc.wikimedia.org/mediawiki-core/master/js/#!/api/mw.widgets.CalendarWidget
https://doc.wikimedia.org/mediawiki-core/master/js/#!/api/mw.widgets.DateInputWidget

Similar to what we have for OOjs UI core widgets like https://doc.wikimedia.org/oojs-ui/master/js/#!/api/OO.ui.ButtonWidget which have a Show Preview and Code Example.