Include domain in rational expression question

Redoing this pull request without the other unwanted commits.

I've added a new solution box to the question whenever you divide by an expression so you have to include the domain condition as part of your answer.

It's formatted using a table isn't isn't ideal especially as tabbing from one box to another goes in an unintuitive order, but it seemed better than creating a lot more divs and trying to line them up.

Addresses issue #43362