StudentQuiz: The marker bullets are overlapping #787208

[danghieu1407]

with the placeholder text in the comment textbox

Hi @timhunt,
This ticket is ready for review.
I have created a new function, setPlaceholder, to set a placeholder when the editor is empty.
I have also added a new condition for the mutation. Previously, when we reloaded the page and then inserted a line break using "Enter", if we deleted the line break and pressed "Space", the mutation would not trigger. To address this, I added a new condition.
Additionally, I have created a regex to handle specific cases. If it matches, it means the data in the editor is empty.
Could you please review these changes? Many thanks.

[timhunt]

Note for future reference: element.dataset.placeholder = placeholder is better than element.attr('data-placeholder', placeholder).

But, I will merge this as is, because the code is consistently using the less good style.