Fix our getTypeOfGroup function

Add in the missing `'sizing'` entry, put the `'text'` entry in the correct
place, and replace `groupToType.ord` (a null value) with `groupToType.mathord`
(something real).

Test Plan:
 - See that `^3+` now puts the correct space before the `+`
 - See the new huxley test works, and nothing else has changed

Auditors: alpert