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Significant refactor of Lint

Simon Peyton Jones requested to merge wip/T17923 into master

Significant refactor of Lint

This refactoring of Lint was triggered by #17923 (closed), which is fixed by this patch. The main change is this. Instead of lintType :: Type -> LintM LintedKind we now have lintType :: Type -> LintM LintedType

Previously, all of typeKind was effectively duplicate in lintType. Moreover, since we have an ambient substitution, we still had to apply the substition here and there, sometimes more than once. It was all very tricky, in the end, and made my head hurt.

Now, lintType returns a fully linted type, with all substitutions performed on it. This is much simpler.

The same thing is needed for Coercions. Instead of lintCoercion :: OutCoercion -> LintM (LintedKind, LintedKind, LintedType, LintedType, Role) we now have lintCoercion :: Coercion -> LintM LintedCoercion

Much simpler! The code is shorter and less bug-prone.

There are a lot of knock on effects. But life is now better.

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