[clangd] Collecting main file macro expansion locations in ParsedAST.
Summary: TokenBuffer does not collect macro expansions inside macro arguments which is needed for semantic higlighting. Therefore collects macro expansions in the main file in a PPCallback when building the ParsedAST instead.
Reviewers: hokein, ilya-biryukov
Subscribers: MaskRay, jkorous, arphaman, kadircet, cfe-commits
Differential Revision: https://reviews.llvm.org/D66928