[clangd] Remove highlightings coming from non topLevelDecls from included files.

Summary: It is possible to write include code from other files so that the decls from there do not become topLevelDecls (For example by including methods for a class). These Decls are not filtered by topLevelDecls and therefore SemanticHighlighting must manually check that every SLoc belongs in the main file. Otherwise there can be highlightings appearing in places where they should not.

Reviewers: hokein, ilya-biryukov

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

Tags: #clang

Differential Revision: https://reviews.llvm.org/D66083

llvm-svn: 368563