[clangd] Return TextEdits from ClangdServer::applyTweak
Instead of tooling::Replacements. So that embedders do not need to store
the contents of the file.
This also aligns better with ClangdServer::rename.
Reviewers: kadircet, hokein
Reviewed By: hokein
Subscribers: MaskRay, jkorous, arphaman, cfe-commits
Differential Revision: https://reviews.llvm.org/D63140