Allow handlers to return integral return codes

[tats-u]

I would like to pass Func<?, int> to RootCommand.SetHandler, but C# does not allow additions of such overloads.
I need a new SetHandlerWithReturnCode method.

[KalleOlaviNiemitalo]

It was already implemented in #2121. Unfortunately, that still hasn't been published to NuGet Gallery.