Allow Swift hosts to handle navigation links

[kiftio]

Summary

Stacked on #851.

Swift had the same split behavior as Android: protocol ec.window.open_request calls consulted onLinkClick, but a raw WKNavigationDelegate navigation to a deep link opened through UIApplication directly.

Apply the existing linkActionProvider to intercepted deep-link navigation before the default external URL handler:

• open preserves the current default behavior.
• handled lets the host own routing.
• cancel blocks the navigation.

This keeps Swift and Android consistent and makes onLinkClick govern both protocol window-open requests and native WebView deep-link navigation.

Tests

• Added coverage that handled and cancel prevent the external URL handler from being invoked for a navigation deep link.
• Ran:

  platforms/swift/Scripts/xcode_run test ShopifyCheckoutKit-Package CheckoutWebViewTests

  93 tests passed.

Diagnostics

Adds debug logging that distinguishes an intercepted raw navigation link from the host or SDK default-handling outcome.

[bitrise]

Install this build

Open Tophat, select your target device, then click Install. Links open on the Mac running Tophat.

SDK	Install
Swift	Install with Tophat

Checkout Kit E2E results

Status	Tags	Target	Platform	OS version tag	Device
✅	launch, checkout-presentation, checkout-completion, buyer-identity, preload	swift	ios	latest	iPhone 15 iOS 27 Beta