[in_app_purchase] Add InAppPurchaseException to platform interface

[mvanbeusekom]

This PR adds the InAppPurchaseException class to the in_app_purchase_platform_interface exception as discussed in this comment: #3841 (comment)

When this is merged I will remove the InAppPurchaseException from the in_app_platform_android implementation that is currently part of PR #3841.

This PR is part of the effort to migrate the in_app_purchase plugin to the Federated plugin architecture: flutter/flutter#78525

If you had to change anything in the flutter/tests repo, include a link to the migration guide as per the breaking change policy.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide and the C++, Objective-C, Java style guides. (Note that unlike the flutter/flutter repo, the flutter/plugins repo does use dart format. See plugin_tool format)
• I signed the CLA.
• The title of the PR starts with the name of the plugin surrounded by square brackets, e.g. [shared_preferences]
• I listed at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy.
  • This change will be part of version 1.0.0 which is already merged into master but not yet published.
• I updated CHANGELOG.md to add a description of the change.
  • This change will be part of version 1.0.0 which is already merged into master but not yet published.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test exempt.
• All existing and new tests are passing.

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[cyanglaz]

LGTM

[mvanbeusekom]

Landing with only "Windows Plugins" step being red.