[local_auth_darwin][UIScene] Add UIScene lifecycle support

[okorohelijah]

Adds support for the new Apple UIScene lifecycle while maintaining backward compatibility with apps that haven't migrated yet.

Fixes flutter/flutter#174411

Pre-Review Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter.
• I signed the CLA.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I linked to at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or I have commented below to indicate which version change exemption this PR falls under¹.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style, or I have commented below to indicate which CHANGELOG exemption this PR falls under¹.
• I updated/added any relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or I have commented below to indicate which test exemption this PR falls under¹.
• All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

Note: The Flutter team is currently trialing the use of Gemini Code Assist for GitHub. Comments from the gemini-code-assist bot should not be taken as authoritative feedback from the Flutter team. If you find its comments useful you can update your code accordingly, but if you are unsure or disagree with the feedback, please feel free to wait for a Flutter team member's review for guidance on which automated comments should be addressed.

Footnotes

1. Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling. ↩ ↩² ↩³

[gemini-code-assist]

Code Review

This pull request adds support for the UIScene lifecycle to the local_auth_darwin plugin, ensuring compatibility with modern iOS apps while retaining support for older apps using the UIApplication lifecycle. This is achieved by adding a sceneDidBecomeActive delegate method and registering the plugin as a FlutterSceneLifeCycleDelegate. The changes also include updating the package version and SDK constraints. My review includes a suggestion to improve code maintainability by reducing duplication.

[vashworth]

Can you also migrate the example app using the app guide? https://docs.flutter.dev/release/breaking-changes/uiscenedelegate#migration-guide-for-flutter-apps

[vashworth]

Suggested change

	#if os(iOS)
	registrar.addApplicationDelegate(instance)
	registrar.addSceneDelegate(instance)
	#endif
	registrar.addApplicationDelegate(instance)
	#if os(iOS)
	registrar.addSceneDelegate(instance)
	#endif

registrar.addApplicationDelegate(instance) is not iOS specific, it also applies to macOS.