[clangd] Use the macro name range as the definition range.

Summary: This also aligns with the behavior of declarations.

Reviewers: sammccall

Reviewed By: sammccall

Subscribers: klimek, ilya-biryukov, jkorous-apple, ioeric, cfe-commits

Differential Revision: https://reviews.llvm.org/D44423

llvm-svn: 327401