Chapter and variant combinations are undefined

[arsalan0c]

The supported chapter and variant combinations are currently defined in cadet-frontend, in the file src/reducers/states.ts at line 227:
https://github.com/source-academy/cadet-frontend/blob/1c7d40933bae38b2b922d98b844ac7d91b3db783/src/reducers/states.ts#L227

Considering the purpose of js-slang, it might be more appropriate for the supported combinations to be defined in js-slang instead and made use of by cadet-frontend.

This would also help #549