[clangd] Enable diagnostic fixes within macro argument expansions.

Summary: This seems like a pretty safe case, and common enough to be useful.

Reviewers: hokein

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

Tags: #clang

Differential Revision: https://reviews.llvm.org/D78338