Do not instantiate meta variables of fixed kind to `ZonkAny` as it often leaks to users of ghc api
## Summary
During zonking GHC instantiates meta variables to `ZonkAny n`. This is an implementation detail that often leaks to users via users of ghc api. Most prominently to hls.
This is bad because
- "zonking" is GHC specific language that is not well known to users
- `ZonkAny` is not defined in any library and cannot be obtained info about, easily. It is also an implementation detail.
## Steps to reproduce
E.g. check the type of `length []` with hls
## Expected behavior
Should not show `ZonkAny` but one of
- an uninstantiated meta variable
- a pretty printed version of `ZonkAny` that looks like a normal variable
- a skolem
## Environment
* GHC version used: n/a
Optional:
* Operating System: n/a
* System Architecture: n/a
issue