[clangd] Correct the file path in Edit::replacements when generating the rename edit.
The file path was set to the file content previously, and it isn't
covered by normal clangd & unittest code path (as we only uses the
offset, length, replacement text).
Subscribers: MaskRay, jkorous, arphaman, kadircet, usaxena95, cfe-commits
Differential Revision: https://reviews.llvm.org/D70828