delite/FormValueWidget

delite/FormValueWidget is a base class for form widgets that have a value, such as a combobox or slider.

It defines two main methods that the subclass should call:

• handleOnInput() - Call this whenever the user changes the value, for example as a slider handle is being dragged.
• handleOnChange() - Call this whenever the user "commits" the value change, typically on pointerup or keyup (in the slider example, releasing the slider handle).