[clangd] Add type boost to fuzzy find in Dex.

Summary:
No noticeable impact on code completions overall except some improvement on
cross-namespace completion.

Reviewers: sammccall, ilya-biryukov

Reviewed By: sammccall

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

Tags: #clang

Differential Revision: https://reviews.llvm.org/D57815

llvm-svn: 353310