RPChoiceAnswerFormat constructor
      
      RPChoiceAnswerFormat({ 
    
- required RPChoiceAnswerStyle answerStyle,
- required List<RPChoice> choices,
Returns an initialized choice answer format with the given ChoiceAnswerStyle
and the set of RPChoices.
Implementation
RPChoiceAnswerFormat({required this.answerStyle, required this.choices})
    : super() {
  questionType = (answerStyle == RPChoiceAnswerStyle.SingleChoice)
      ? RPQuestionType.SingleChoice
      : RPQuestionType.MultipleChoice;
}