[clangd] Boost scores for decls from current file in completion
Summary: This should, arguably, give better ranking.
Reviewers: ioeric, sammccall
Reviewed By: sammccall
Subscribers: mgorny, klimek, MaskRay, jkorous, mgrang, cfe-commits
Differential Revision: https://reviews.llvm.org/D46943
llvm-svn: 333906