…anionAd` (#7873)

…7887)

This PR contains the preliminary implementations for handling [purchases](https://developer.apple.com/documentation/storekit/product/3791971-purchase) and [transactions](https://developer.apple.com/documentation/storekit/transaction) 

Of note, as of StoreKit 2, the [result of a call to a purchase will only return a Transaction](https://developer.apple.com/documentation/storekit/product/purchaseresult) when the purchase is successful. If the status of purchase is pending, or cancelled, nothing will be returned. 

This is in contrast to StoreKit 1, where developers could check the state of a Transaction with [TransactionState](https://developer.apple.com/documentation/storekit/skpaymenttransaction/1411275-transactionstate). This means that migrating to StoreKit 2 will require developers to update their handling of transactions accordingly. 

Relands #7574

…7774)

- ShellExecuteW does not handle file: urls that contain %-encoded UTF-8 strings correctly.  %-encoded ASCII
   strings are handled correctly, as are file "urls" that contain Unicode strings in its path component.
- This change perform URL decode on file: urls before passing to ShellExecuteW.

Fixes flutter/flutter#156790

Add structured types and convert implementations to use typesafe method
calls for platform methods from Dart to native side.

Android analog of #6601

Part of flutter/flutter#117905

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