feat(quiz): allow revealing correct answers on success

[huyenltnguyen]

Checklist:

• I have read freeCodeCamp's contribution guidelines.
• My pull request has a descriptive title (not a vague title like Update index.md)

This PR:

• Updates the useQuiz hook to pass the correct status to the correct answer
• Adds a showCorrectAnswersOnSuccess prop to useQuiz
• Is related to Answer of quiz in Full stack curriculum freeCodeCamp#58394

Screenshot

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At the moment, the Quiz component only shows the validation status (correct or incorrect) on the selected answer. We've got a request that if the user has passed the quiz but got some questions wrong, they should be able to see what the correct answers are.

The validation status is implemented here:

ui/src/quiz/use-quiz.ts

Lines 69 to 81 in 6b83ce3

	// Only pass validation to the selected answer
	if (answer.value === question.selectedAnswer) {
	validation =
	answer.value === question.correctAnswer
	? {
	state: "correct",
	message: validationMessages.correct,
	}
	: {
	state: "incorrect",
	message: validationMessages.incorrect,
	};
	}

Instead of just adding a grade >= passingGrade conditional, I'm using a showCorrectAnswersOnSuccess prop as well. I want to give the component some flexibility but I'm not sure if we really need this prop. Currently we only have quizzes and exams as the consumers:

• Quizzes: we do want to show correct answers on success
• Exams: (I believe) we don't even show the validation status on the selected answers

Though, if we just have the grade >= passingGrade conditional, the changes in this PR are breaking changes and should go into v4.

[huyenltnguyen]

So we currently are:

• Using prevQuestions to build a new questions array (updatedQuestions), with validation status added to the answers
• Use updatedQuestions to compute correctCount
• Then, use correctCount to compute grade

In order to achieve the new behavior, updatedQuestions needs to have access to grade, so I have to change the definition order.

Since prevQuestions contains sufficient information to determine the correct selections, I'm using it to compute correctCount and grade instead (which removes their dependence on updatedQuestions).