Input fields accept arbitrary widgets

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Currently, the Quiz widget allows users to insert arbitrary widgets into any of the answer input fields. As a consequence, users can insert another Quiz widget within a Quiz answer, leading to unintended nesting scenarios. This behavior is neither intuitive nor expected.

Steps to reproduce:

1. Add a Quiz widget to a page.

2. In the answer input field, attempt to insert another Quiz widget.

3. Notice the Quiz widget successfully nests inside the original Quiz.

Expected behavior:
The Quiz widget should restrict input fields to basic formatting, explicitly preventing insertion of other complex widgets like nested quizzes.