flutter#29572: DropdownButton Icon customizability

flutter#29183: Implement labelPadding configuration in TabBarTheme

flutter#21834: Add shapeBorder option on App Bar

flutter#28163: [Material] Add ability to set shadow color and selected shadow color for chips and for chip themes

flutter#27711: Make extended FAB’s icon optional

flutter#28159: [Material] Expand BottomNavigationBar API (reprise)

flutter#27973: Add extendBody parameter to Scaffold, body MediaQuery reflects BAB height

flutter#30390: [Material] Update slider and slider theme with new sizes, shapes, and color mappings

flutter#29390: Make expansion panel optionally toggle its state by tapping its header.