Command Bar Updates

[bdlukaa]

• feat: Added CommandBarButton.closeAfterClick (Fixes Close Flyout after click CommandBarButton #1149)
• feat: Added FlyoutController.showFlyout.buildTarget (Fixes Possibility for Flyout Target to be tappable when flyout is shown #1173)
  Primary items of the command bar are now accessible through the secondary flyout.
• fix: CommandBar secondary menu preferred placement mode
• feat: Added FlyoutController.close
• feat: CommandBarState is now accessible, making it possible to open/close the secondary flyout

  final commandBarKey = GlobalKey<CommandBarState>();
  
  CommandBar(
    key: commandBarKey, 
    ...,
  ),
  
  commandBarKey.currentState?.toggleSecondaryMenu();
  commandBarKey.currentState?.secondaryFlyoutController.close();

Pre-launch Checklist

• I have updated CHANGELOG.md with my changes
• I have run "dart format ." on the project
• I have added/updated relevant documentation