public struct FeaturePurchaseRequirements
This type provides information about the purchases required for a single conditional feature.
You can use this at runtime to establish which purchases you need to show to the user to enable them to unlock a feature.
The set of all purchases required that must be met for the feature to be available, which have not already been purchased. This includes purchases for which we know the user has not purchased them (or failed, or become invalid), and those for which we have no status information yet.
public let requiredToUnlock: Set<PurchaseRequirement>