cupertino component tracker

TODO: audit
TODO: add missing components, e.g. iOS Modal Sheets, Menus, different styles of pickers, etc. See links with [-] in this issue's source

¹: HIG guidelines link out to UIKit and SwiftUI developer docs. Look for "For developer guidance, see...".
²: This table includes a subset of all cupertino widgets. It does not include:

• building-block widgets e.g. CupertinoDialogAction, used to build these components
• non-component widgets e.g. CupertinoPageTransition and CupertinoPageScaffold.

See also

• Flutter-SwiftUI widget catalog, for audit and testing purposes
• flutter_platform_widgets, a package which has implemented 24 platform adaptive widgets
• https://docs.flutter.dev/development/ui/widgets/cupertino, a mostly complete view of all cupertino widgets
• https://github.com/flutter/flutter/projects/124, "iOS Platform - Cupertino widget review"
• ☂️ Material 3 iOS Adaptations #94821

cc @jmagman