[clang] Store code completion token range in preprocessor.

Summary:
This change is to support a new fature in clangd, tests will be send toclang-tools-extra with that change.

Unittests are included in: https://reviews.llvm.org/D50449

Reviewers: ilya-biryukov

Reviewed By: ilya-biryukov

Subscribers: ioeric, MaskRay, jkorous, arphaman, cfe-commits

Differential Revision: https://reviews.llvm.org/D50443

llvm-svn: 339540