Filter tax-insufficient saved payment methods (MOBILESDK-4697)

[cttsai-stripe]

Summary

On the Checkout Session path, when automatic tax uses billing as its tax address source, filter out saved payment methods whose billing address lacks the country-specific fields Stripe Tax needs. This prevents offering a saved payment method that would hard-fail at confirm.

This PR is stacked after the new-payment-method work in #13713 and #13718. It reuses the shared country requirements from #13717 without mixing saved-payment-method behavior into MOBILESDK-4667.

Motivation

Verified against pay-server: FinalizePaymentTaxes recomputes tax from the selected payment method billing address at confirm and raises checkout_automatic_tax_confirmation_failure (subscription mode: billing_automatic_tax_unrecognized_customer_location), HTTP 400, on any non-complete tax status. There is no silent zero-tax path. That confirm guard is not payment-method-type gated, so the filter intentionally applies to all saved-payment-method types.

Email does not need client-side sufficiency validation; the backend handles it. This change validates only the billing address required to compute tax for the payment method country.

Implementation:

• Add PaymentMethod.hasSufficientBillingDetailsForAutomaticTax() using the shared country requirements from Share automatic-tax billing address primitives (MOBILESDK-4667) #13717.
• Consult it in DefaultPaymentMethodFilter for every saved payment-method type.
• Thread the Checkout Session-only requirement from PaymentMethodMetadata through CustomerState into FilterParams; other PaymentSheet integrations remain no-ops.

Saved-card billing-details editing remains separate and standalone in #13506.

JIRA: MOBILESDK-4697. iOS sibling: MOBILESDK-4698.

Testing

• Added tests
• Modified tests
• Manually verified

Targeted unit tests passed:

• BillingDetailsValidationTest: country-specific address sufficiency.
• DefaultPaymentMethodFilterTest: gating, null/incomplete addresses, country boundaries, and non-card saved methods.
• CreateCustomerStateTest: propagation of the automatic-tax billing-address requirement.

The focused PaymentSheet unit-test set, :paymentsheet:detekt, and :paymentsheet:apiCheck passed.

Screenshots

N/A - no new UI surface; this removes unusable saved payment methods from the list.

Changelog

N/A - Checkout Session is behind @CheckoutSessionPreview; the implementation is internal/library-group restricted.