[clangd] Add distinct highlightings for static fields and methods

Reviewers: hokein, ilya-biryukov, jvikstrom

Reviewed By: hokein

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

Tags: #clang

Differential Revision: https://reviews.llvm.org/D66828

llvm-svn: 370429