Summary:
There was a rather annoying corner case where splicing poly-kinded
Template Haskell declarations could trigger an error muttering about
`TypeInType` not being enabled, whereas the equivalent non-TH code would
compile without issue. This was causing by overzealous validity check in the
renamer, wherein failed to distinguish between two different `Exact` names
with the same `OccName`. As a result, it mistakenly believed some type
variables were being used as both type and kind variables simultaneously! Ack.

This avoids the issue by simply disabling the aforementioned validity check
for Exact names. Fixes #12503.

Test Plan: ./validate

Reviewers: austin, bgamari, goldfire

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D3022