Replace logic in NewTyp::mkTypForConstrainedType with a recursive AST visitor

[secure-sw-dev-bot]

This issue was copied from checkedc/checkedc-clang#48

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The logic in NewTyp::mkTypForConstrainedType is ugly and probably wrong in some cases. It should be replaced with either a ginormous switch statement (which is more intuitive from an ML-persons point of view, but not LLVM idiomatic) or a RecursiveASTVisitor (which is ugly from an ML-persons point of view because functionality is smeared across a bunch of tiny functions, but is LLVM idiomatic).

[secure-sw-dev-bot]

Comment from @awruef:

The logic in NewTyp::mkTypForConstrainedType has been replaced with another class (ConstraintVariable) however, that infrastructure has a need for the same change.

[secure-sw-dev-bot]

Comment from @dtarditi:

We aren't likely to come back and do this for the rewriter. Closing this issue.