[clangd] Update semanticTokens support to reflect latest LSP draft

Summary: Mostly a few methods and message names have been renamed.

Reviewers: hokein

Subscribers: ilya-biryukov, MaskRay, jkorous, arphaman, kadircet, usaxena95, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D83556