Required doesnt want an @anymore

[Eric Isensee]

When converting to Dart and use "Make all properties required" it does add an @ infront of required. That isnt used anymore in Dart and Flutter.

[Duncan Pullen]

To help, currently it creates the following for Dart conversion:

CustomCodeValue({
        @required this.codeValue,
        @required this.display,
        @required this.codeSet,
        @required this.codeValueId,
    });

Should be:

    CustomCodeValue({
        required this.codeValue,
        required this.display,
        required this.codeSet,
        required this.codeValueId,
    });

[Nato Boram]

Duplicate of #1755