[Android] Rename CheckoutEventProcessor → CheckoutListener, drop stale callbacks

[tiagocandido]

What changes are you making?

Renames CheckoutEventProcessor → CheckoutListener on Android (with DefaultCheckoutEventProcessor → DefaultCheckoutListener) and drops two methods now owned by the protocol layer:

• onCheckoutCompleted → use CheckoutProtocol.complete
• onCheckoutLinkClicked → use CheckoutCommunicationClient.openExternalUrl(...)

Removes the legacy code paths that fed those callbacks: the COMPLETED case in CheckoutBridge, the external-link branch in CheckoutWebView's URL override, and the legacy intent-launching defaults on DefaultCheckoutEventProcessor.

A few behavior tweaks to keep parity with the previous Android implementation:

• ec.complete now invalidates the preload cache (was done by the old onCheckoutViewComplete path)
• ec.window.open_request no longer filters URI schemes at the bridge — any URI is forwarded to openExternalUrl(...) so apps can handle mailto:/tel:/custom schemes themselves
• When openExternalUrl(...) is absent or returns false, the bridge returns a JSON-RPC error instead of acknowledging success
• FallbackWebView keeps confirmation-page detection and forwards a partial ec.complete (order ID only) to the client, so recovered checkouts still notify the host app. Follow-up: wire the full ECP bridge into the fallback path.

Internal field/class names follow the rename for consistency (CheckoutWebViewEventProcessor → CheckoutWebViewListener, eventProcessor → listener throughout). README and lib/api/lib.api are updated.

Note: The React Native Android wrapper extends DefaultCheckoutEventProcessor and overrides onCheckoutCompleted — it will need a follow-up PR to rename the extends clause and route completion through CheckoutProtocol.complete.

How to test

• ./gradlew :lib:test :lib:apiCheck :lib:detekt :lib:lintRelease
• Build the MobileBuyIntegration sample and complete a checkout end-to-end; confirm the CheckoutProtocol.complete handler in CartViewModel fires (clears cart and pops back to the product screen)

---

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 relevant platform README (platforms/swift/README.md and/or platforms/android/README.md)

[tiagocandido]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• [Android] Rename CheckoutEventProcessor → CheckoutListener, drop stale callbacks #132 👈 (View in Graphite)
• [Swift] Restore CheckoutDelegate with trimmed lifecycle API #131
• feat: remove checkout lifecycle from react-native #116
• feat(react-native): use local android/swift project references #115 : 1 other dependent PR (#119 )
• feat(protocol): add typescript interfaces #114
• main

This stack of pull requests is managed by Graphite. Learn more about stacking.