fix(iOS): drain UISceneConnectionOptions on cold launch (#21362)

[koblavi]

Summary

Fixes #21362 — the cold-launch path of #17600 (#18005 only addressed the warm path).

When the iOS app uses scene-based lifecycle (iOS 13+), Apple delivers cold-launch user activities and URL contexts via UISceneConnectionOptions on scene:willConnectToSession:options: — not via the warm-path selectors scene:continueUserActivity: or scene:openURLContexts:. AvaloniaSceneDelegate ignored connectionOptions entirely, so cold-launching the app from a Universal Link or custom-scheme URL dropped the URL on the floor.

The user's subscriber to IActivatableLifetime.Activated then only saw the base ActivatedEventArgs raised by the foreground transition (OnLeavingBackground), never a ProtocolActivatedEventArgs with the URL.

Change

AvaloniaSceneDelegate.WillConnect, after creating the window, drains both connectionOptions.UserActivities and connectionOptions.UrlContexts through the existing IAvaloniaAppInternalDelegate paths.

Also adds scene:openURLContexts: so warm custom-scheme URLs work under scene lifecycle — previously these were silently dropped too because application:openURL: on the AppDelegate is not called when scenes are in use (a smaller pre-existing bug surfaced by this same investigation).

The IAvaloniaAppInternalDelegate interface gains an OpenUrl(NSUrl) method so the scene delegate can route URL contexts through the same code path the existing application:openURL:options: AppDelegate handler uses. The AppDelegate's public OpenUrl selector method is refactored to a one-liner delegating to the explicit interface impl — no behaviour change for the AppDelegate-only path.

Test plan

The Avalonia.iOS.UnitTests / Avalonia.IntegrationTests.iOS paths in sparse-checkout return empty, so iOS scene-lifecycle test scaffolding doesn't currently exist in the repo to model from. Happy to add a test if maintainers can point at a fixture pattern.

Manual repro (from issue):

1. Avalonia 12.0.2 iOS app with Associated Domains entitlement (applinks:<your-domain>) + matching AASA served.
2. Subscribe to IActivatableLifetime.Activated in App.Initialize, log ProtocolActivatedEventArgs.Kind vs the bare type name.
3. Build signed dev IPA, install to physical device. Force-quit the app (this is critical — warm activations already work).
4. Tap a https://<your-domain>/... Universal Link from Messages / Mail.
5. Before this fix: Activated fires with base ActivatedEventArgs, no URL surfaces. Device console: OnActivated fired: kind=ActivatedEventArgs.
6. After this fix: Activated fires with ProtocolActivatedEventArgs.Kind == OpenUri carrying the URL.

For URL contexts (custom schemes via scene lifecycle): same flow, with a myapp://... URL instead of a Universal Link — before this PR these fall through entirely under scene lifecycle; after, they route to ProtocolActivatedEventArgs like the AppDelegate path.

References

• [iOS] Cold-launch Universal Link raises base ActivatedEventArgs (no URL) — #17600 cold path still broken in 12.0.2 #21362 — original bug report (this PR)
• Activation with universal link not working as expected on iOS #17600 — original Universal Link bug
• Support activation with universal links #18005 — earlier fix that only handled the warm path

🤖 PR drafted with assistance from Claude Code

[avaloniaui-bot]

You can test this PR using the following package version. 12.1.999-cibuild0065551-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[cla-avalonia]

• All contributors have signed the CLA.

[koblavi]

@cla-avalonia agree

[koblavi]

For triage when a maintainer gets to this — suggested labels:

• bug (cold-launch URL drop is a regression vs the documented behavior of IActivatableLifetime)
• os-ios

Ping @timunie since you already engaged on the parent issue #21362.

[MrJul]

LGTM!