Add engine group constructor in FlutterViewConrtroller

[luckysmg]

We can use like this:

let engineGroup = FlutterEngineGroup(name: "io.flutter", project: nil)
window?.rootViewController = FlutterViewController(engineGroup: engineGroup, nibName: nil, bundle: nil, entrypoint: nil, libraryURI: nil, initalRoute: nil)

List which issues are fixed by this PR. You must list at least one issue.
flutter/flutter#72742

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[gaaclarke]

The code is correct and it makes sense, but I think we should error on the side of keeping the API as simple as possible. This convenience function is something you could just have in your project and isn't something that is required to be in the Flutter API.

@xster I know you write the issue this fixes, what do you think about this now?

[xster]

Thanks. I think this is helpful. We should keep parity between the platforms however. There should be an Android solution as well (though I acknowledge it'll be a lot more complicated than iOS).

[xster]

If

[luckysmg]

done

[xster]

Describe the ownership of the resulting FlutterEngine from this API. e.g. if you pop this view controller, the engine is permanently gone?

[luckysmg]

done

[ColdPaleLight]

Thanks. I think this is helpful. We should keep parity between the platforms however. There should be an Android solution as well (though I acknowledge it'll be a lot more complicated than iOS).

The Android solution will be completed soon, and we will file a PR in the next few days :) .

[luckysmg]

@xster
The Android Related PR is here:#29293

[luckysmg]

Close this PR and later open a new PR about this feature