[MBL-1373] ValidateCheckout Before Completing Checkout With ApplePay

[scottkicks]

📲 What

Calls ValidateCheckout mutation after ApplePay Context completes and before CompleteOnSessionCheckout

🤔 Why

We should be validating the current late pledge checkout for ApplePay pledges like we do for Stripe pledges.

🛠 How

When the ApplePay sheet completes, didCreatePaymentMethod is called and we pass our ApplePayParams object back to the ViewModel to complete the checkout. This method returns a StripePayments.STPPaymentMethod with an id (stripeId) that we need to validate the checkout. So, we'll use that ID to call ValidateCheckout before trying to complete the checkout.

👀 See

No visible changes

✅ Acceptance criteria

• ApplePay Late Pledges still work
• If ValidateCheckout fails, an error message banner is shown
• The processing view is still shown until the backing is complete

[ifosli]

A couple comments but not blocking for this pr. However, please make sure you actually test this in prod if you haven't already! With the release timeline, I'm okay with just testing that in the testflight build if that's easier and doing a rollback if we need to, but let's make sure any apple pay changes are thoroughly tested before they're released to our users.

[amy-at-kickstarter]

Also LGTM.

[scottkicks]

@ifosli Noted in regression that we should thoroughly test this in TestFlight before releasing. I also cleaned up the ApplePayParams stuff. Good call out!