Moved QualTypeNames.h from Tooling to AST.

Summary:
For code reuse in SemaCodeComplete.
Note that the tests for QualTypeNames are still in Tooling as they use
Tooling's common testing code.

Reviewers: rsmith, saugustine, rnk, klimek, bkramer

Reviewed By: rnk

Subscribers: cfe-commits, mgorny

Differential Revision: https://reviews.llvm.org/D39224

llvm-svn: 317676