`TpData` should have tags and params as two separate lists

[davidweichiang]

Come to think of it, if DefCtor and DefData have tags and params as two separate [Var]s (which makes sense), then TpData should have tags and params as two separate lists as well ([Var] and [Type] I guess).

Originally posted by @ccshan in https://github.com/diprism/perpl/issues/79#issuecomment-1198845332

[davidweichiang]

I still think that because tags are used only during type inference, it'd be nicer not to have to drag that (usually empty) list of tags through all the other phases. I'm still hoping that we can distinguish tag and type variables as different cases so we can store them in a single list everywhere...

[ccshan]

But the single list (or both lists) are empty after monomorphization, right?

[davidweichiang]

RIght.

[davidweichiang]

This also affects TmCase and the return value of ctxtLookupType2 (sorry for my terrible naming).

[davidweichiang]

And TmVarG

[davidweichiang]

Closed by #102