Is there an existing issue for this?

• I have searched the existing issues
• I have read the guide to filing a bug

Steps to reproduce

1. Create a Flutter project and add this to your pubspec.yaml:
   in_app_purchase: 3.1.5
2. In your test app access members GooglePlayProductDetails.skuDetails, PurchaseWrapper.skus and SkuDetailsWrapper
3. Make sure the project builds successfully.
4. Update pubspec.yaml as follows:
   in_app_purchase: ^3.1.5
5. Upgrade the packages in your project with:
   flutter packages upgrade

Expected results

The project should build successfully also after upgraded packages. If there were breaking changes the package should increase its major/minor version number and document the breaking changes in the change log.

Actual results

The build fails as there are breaking changes, but only the patch number of the package version was increased. Errors include:

The getter 'skuDetails' isn't defined for the type 'GooglePlayProductDetails'.
The getter 'skus' isn't defined for the type 'PurchaseWrapper'.
Undefined class 'SkuDetailsWrapper'.

There could be also other breaking changes, I listed here only those which I see in my project. The current change log of in_app_purchase does not mention any breaking changes after 3.1.5.

Code sample

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