Re-commit r183466 with a fix to make the TypeLoc casting machinery work

Re-commit r183466 with a fix to make the TypeLoc casting machinery work
correctly in the presence of qualified types.

(I had to change the unittest because it was trying to cast a
QualifiedTypeLoc to TemplateSpecializationTypeLoc.)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@183563 91177308-0d34-0410-b5e6-96231b3b80d8