internal ConvertOptionsBuilder(ConvertOptionsBuilder other, Type targetType, ConverterDelegate converter)
 {
     _optionSets = other._optionSets;
     _converters = other._converters.SetItem(targetType, converter);
 }
 internal ConvertOptionsBuilder(ConvertOptionsBuilder other, params OptionSet[] newOptions)
 {
     _optionSets = newOptions.Aggregate(other._optionSets, (dict, option) => dict.SetItem(option.GetType(), option));
     _converters = other._converters;
 }