Fix crash in lazy protocol witness table accessor for type PayWithApplePayButtonLabel on iOS 18

[fynnrhm]

What changes are you making?

Summary

• keep the UIKit-backed Apple Pay button implementation in place
• expose native PassKit button type/style values through .applePayLabel(_:) and .applePayStyle(_:)
• remove the SwiftUI PayWithApplePayButton* to PKPaymentButton* mapping layer and update samples/docs

Crash context

This is intended to avoid the iOS 18 cart initialization crash seen while resolving the mapped SwiftUI Apple Pay label/style values:

Exception 1, Code 1, Subcode 12 > KERN_INVALID_ADDRESS at 0xc
libswiftCore swift::_getWitnessTable
PayWithApplePayButtonLabel.pkPaymentButtonType.getter (ApplePayButton.swift:171)
Internal_ApplePayButton.body.getter (ApplePayButton.swift:140)
SwiftUICore ViewBodyAccessor.updateBody

By accepting PKPaymentButtonType and PKPaymentButtonStyle directly, the representable receives native PassKit values without the extra computed-property mapping on the SwiftUI types.

Verification

• scripts/xcode_run test ShopifyCheckoutSheetKit-Package ShopifyAcceleratedCheckoutsTests/ApplePayIntegrationTests
• Scripts/build_samples
• git diff --check

Before you merge

Important

• I've added tests to support my implementation
• I have read and agree with the Contribution Guidelines.
• I have read and agree with the Code of Conduct.
• I've updated the README.

Releasing a new version of the kit?

• I have bumped the version number in the podspec file.

Releasing a new major version?

• I have bumped the version number in the README.

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