T3452 - support function($h,$w){} style constraints in PJS

Summary:
I made this possible in structured a long time ago. But there were a few assumptions in
liveEditor which were breaking it.

Test Plan:
- Complete H for hopper
- Add new style constraint to test challenge
- Se new constrinat work

Reviewers: john, pamela

Subscribers: #cs

Maniphest Tasks: T3452

Differential Revision: https://phabricator.khanacademy.org/D15028