Use case

There's no macOS implementation for in_app_purchase.

I added that and you can view the PR here: flutter/plugins#4313

Proposal

Because the Plugin Developers added a platform_interface to in_app_purchase, it is easily possible now to add a new platform as clean as possible, so I tried to do that here. If you have any concerns or questions, please leave a comment in the PR or here.

Thanks :)