public static extern TOutput[] ConvertAll <TInput, TOutput>(TInput[] array, Converter <TInput, TOutput> converter);
public List <TOutput> ConvertAll <TOutput>(System.Converter <T, TOutput> converter) => _list.ConvertAll <TOutput>(converter);
// ECMA docs use <T,U> instead of <TInput,TOutput> --> map them.
public static TOutput[] ConvertAll <TInput, TOutput> (TInput[] array, Converter <TInput, TOutput> converter)
{
throw new InvalidOperationException();
}