move `ProgramArgsExtensions.WriteOutputToFile` to core

[BryanWilhite]

move this over from Songhay.Player:

//see https://stackoverflow.com/a/5515894/22944
public static void WriteOutputToFile(this ProgramArgs args, Stream stream)
{//TODO: move to Core
    var outputFile = args.GetOutputPath();

    using (var fileStream = File.Create(outputFile))
    {
        stream.Seek(0, SeekOrigin.Begin);
        stream.CopyTo(fileStream);
    }
}