New widget type for quantity field

At present the quantity field is a Decimal field that it cannot support a select list as a widget.

I would like to propose a new widget plugin for decimal fields that used a select list element.

I efine a custom widget plugin for decimal fields that used a select list element, primary advantage of this is that you then have a UI based way to observe the widget (the form mode configuration for the order item type) and way to differentiate on which order item types to use that widget vs. another

At present to get round this to make better UI we add a plus and minus button to the widget similar approach to https://jsfiddle.net/polaszk/1oyfxoor/