[ObjC] Fix non-canonical types preventing type arguments substitution.

`QualType::substObjCTypeArgs` doesn't go past non-canonical types and as
the result misses some of the substitutions like `ObjCTypeParamType`.

Update `SimpleTransformVisitor` to traverse past the type sugar.

Reviewers: ahatanak, erik.pilkington

Reviewed By: erik.pilkington

Subscribers: jkorous, dexonsmith, cfe-commits

Differential Revision: https://reviews.llvm.org/D57270

llvm-svn: 354164