Show student's selected answer in ExercisePreview component

[Dantemss]

https://openstax.atlassian.net/browse/CORE-933

[Dantemss]

There are some things here that need to be regression tested:

• We used to print an nbsp when answers were not being labeled (not in ExercisePreview), I turned that off
• Correct answers were always filled bubbles, now they can be unfilled if they were not selected

[RoyEJohnson]

Everything looks reasonable to me, but I'm not familiar with the issues you're addressing. I added Josiah as a reviewer; if you need my approval later, I'll do that.

[jivey]

@Dantemss The props are a bit arcane but I thought we did have a way to show correct-but-not-selected bubbles if the answer_id didn't match the correct_answer_id:

[jivey]

Looks fine to me, but as you mentioned will need some regression testing rendering inside assessments with real data.

[Dantemss]

@jivey there was code trying to set styles to invert/not invert the correct answer bubble already, but then the styles in https://github.com/openstax/assessment-components/pull/99/files#diff-a4976d2d79d094466a881e76ee36ad5b4e25305bef76673a0b7f6046099b85adL92 would override everything