`CupertinoElevatedButtonData` should allow to set the `primaryContrastingColor`

[martin-braun]

CupertinoElevatedButtonData.color is useful to change the background of a PlatformElevatedButton on Cupertino when cupertino.originalStyle: false. However when trying to change the foreground, nothing can be done.

CupertinoElevatedButtonData should allow to set the primaryContrastingColor that would get passed in here:

flutter_platform_widgets/lib/src/platform_elevated_button.dart

Line 194 in 216d5e2

data: themeData.copyWith(primaryColor: color),

We might just call it contrastingColor. The only way to bypass this issue right now is to either wrap PlatformElevatedButton into your own CupertinoTheme or modify the colors of the children directly.