[iOS/StoreKit2] Different error handling for purchase failures

[uncoolclub]

I noticed different error handling behaviors in StoreKit2 purchase flows. Is this an intended behavior or a potential issue?

In RNIapIosSk2.swift:

1. For invalid product ID:

else {
    reject("E_DEVELOPER_ERROR", "Invalid product ID...", nil)
    // No purchase-error event emitted
}

2. For user cancellation:
```swift
case .userCancelled:
    let err = [
        "code": IapErrors.E_USER_CANCELLED.rawValue,
        // ...
    ]
    reject(IapErrors.E_USER_CANCELLED.rawValue, "User cancelled the purchase", nil)
    // No purchase-error event emitted

3. But for transaction verification failures:

if self.hasListeners {
    let err = [
        "code": IapErrors.E_TRANSACTION_VALIDATION_FAILED.rawValue,
        // ...
    ]
    self.sendEvent?("purchase-error", err)
    self.sendEvent?("iap-transaction-updated", ["error": err])
}

This leads to inconsistent error handling in JavaScript:

Errors like invalid product ID and user cancellation can only be caught in try-catch blocks
Transaction verification errors update currentPurchaseError through events
This makes it difficult to handle purchase errors in a unified way

Is this intended behavior? If not, I think we should either:

1. Emit both events and rejections for all purchase errors
2. Document the different error handling mechanisms

Screenshots:

1. Using Storekit2
   only reject

currentPurchaseError returned undefined

2. Using Storekit1

currentPurchaseError returned error object