[clangd] Fix a crash when renaming operator.

Summary:
The renamelib uses a tricky way to calculate the end location by relying
on decl name, this is incorrect for the overloaded operator (the name is
"operator++" instead of "++"), which will cause out-of-file offset.

We also disable renaming operator symbol, this case is tricky, and
renamelib doesnt handle it properly.

Reviewers: ilya-biryukov

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

Tags: #clang

Differential Revision: https://reviews.llvm.org/D67607

llvm-svn: 371971