[clang][AST] Add an AST matcher for deducedTemplateSpeializationType.

Summary:
misc-unused-using clang-tidy check needs this matcher to fix a false
positive of C++17 deduced class template types.

Reviewers: gribozavr2

Reviewed By: gribozavr2

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D73869