[clangd] Add a flag to clangdServer rename function to control whether we want...

[clangd] Add a flag to clangdServer rename function to control whether we want format the replacements.

Summary:
This would allow clangd embedders to use the ClangdServer::rename for other
purposes (highlighting all the occurrences of the symbol in prepare
stage).

Reviewers: sammccall, ilya-biryukov

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

Tags: #clang

Differential Revision: https://reviews.llvm.org/D64481

llvm-svn: 365631