Avoid non-deterministic type comparison

[adamgundry]

GhcApi.Compare uses nonDetCmpType, which can given different results between runs. it would be nice to avoid this. Most of the time we don't actually encounter arbitrary Types in Atoms, though, unless the user is doing something very weird.

coxswain has something in this direction that might be helpful: https://github.com/nfrisby/coxswain/blob/bfd5777964a5b4ba64e1bcc4cf18df1c9d8fc558/coxswain/src/LowLevel.hs#L115