Wildcards in type synonyms

[ÉRDI Gergő]

On Mon, 25 Jul 2022, Richard Eisenberg wrote:

> I see this substitution as happening before any type-checking, so zonking shouldn't be an issue. That is, I would expect a
>
> substHsTy :: UniqFM Name (HsType GhcRn) -> HsType GhcRn -> HsType GhcRn
>
> to do the work, entirely before type-checking.

If I were to do this fully during renaming, how do I even find out that a 
`Name` refers to a type macro? During typechecking I can look up the `TyThing`,
see if it's a `MacroTyCon`, and get the rhs from that. But I don't think we store
anything about already-renamed declarations during renaming the same way 
we store info about already-typechecked things during typechecking in 
`tcg_type_env`.

It sounds awfully special-case to store these type macros in a new field 
of `TcGblEnv` instead of as just another kind of `TyCon`.