- Added complete support for showCheckmark to ChipThemeData.
- Removed build method checks for ThemeData.chipTheme, as that is
  already handled by ChipTheme.of().

* Update parameters to the `styleFrom` button methods.

* Updated the Flutter fix data to point to this PR.

* Updated handling of background color to better maintain backwards compatibility with previous API.

* Impl

* Fix build

* Add test