Add application(_:continue:restorationHandler:) on macOS

[rnl-veolys]

Use case

I maintain a plugin (app_links) to allow deep linking on all platforms .
With the current macOS embedder shipped with Flutter 3.19, we can only/mostly handle notification based delegations.

In my case, I need to access application(_:continue:restorationHandler:) to allow universal link handling (as on iOS).
https://developer.apple.com/documentation/appkit/nsapplicationdelegate/1428471-application

This would simplify setup for developers as they wouldn't add themselves the override in their own native code base.

Proposal

There's no workaround here that can be implemented by other packages.

application(_:continue:restorationHandler:) should be forwarded by the engine.