SelectableHtmlWidgetFactory constructor Null safety

1. smooth_app
2. smooth_html_widget
3. SelectableHtmlWidgetFactory
4. SelectableHtmlWidgetFactory constructor

SelectableHtmlWidgetFactory class

1. Constructors
2. SelectableHtmlWidgetFactory
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. noSuchMethod
8. toString
9. Operators
10. operator ==