Move clang/Tooling/Core/Lookup.h to clang/Tooling/Refactoring/Lookup.h

This allows removing the clangAST dependency from libclangToolingCore and
therefore allows clang-format to be built without depending on clangAST.
Before 1166 files had to be compiled for clang-format, now only 796.

Reviewed By: bkramer

Differential Revision: https://reviews.llvm.org/D89708