Feature to add hasChange or previousValue on FormControl

[KabindraKattel]

It would be easier and nice if you include previousValue or hasChange to the formControl so that if an action should be done depending upon previous value or hasChange could be done.

[vasilich6107]

@KabindraKattel check reactive_forms_lbc package specially crafted for reactive_forms

it has an ability to access prev value

https://github.com/artflutter/reactive_forms_widgets/blob/master/packages/reactive_forms_lbc/example/lib/main.dart#L166