Use filter for the corrected typed text.

Add filter so add-ons can cleanly modify the red/green corrected version of a typed answer.

I have already written two add-ons that both monkey-patch this `typeAnsAnswerFilter()` function where the `correct()` is called. Like this these add-ons would be much cleaner.

Here, too, the card is passed along so the add-ons can get an idea what is going on. (My add-ons only do their own correcting when the field had the right name.)