Lint types created by newFamInst
In #15012 (closed), we observed a terrible failure resulting from
newFamInst creating a type family instance with an unbound type variable on the right-hand side. What's worse,
-dcore-lint didn't catch it! Let's fix that by calling
lintType on the types involved in
A wrinkle in this plan is that
lintType currently expands all type synonyms, but the offending type in #15012 (closed) had the unbound variable occur in a type synonym application, so expanding type synonyms would make this naughtiness seemingly vanish (from Core Lint's perspective). We should configure
lintType so that one can control its type synonym expansion behavior.