[clangd] Fix undefined behavior when generating error message at rename with an invalid name

`Message()` lambda uses `Reason.Details` as an input parameter for `llvm::formatv()`, but `Reason` in `Message()` is a local object.
Return value of `llvm::formatv()` contains references to its input arguments, thus `Message()` returns an object which contains a reference to `Details` field of the local object `Reason`.
This patch fixes this behavior by passing `Reason` as a reference to `Message()` to ensure that return value of `Message()` contains references to alive object and also prevents copying of `InvalidName` structure at passing it to `makeError()`.

Provided test passes on Linux+GCC with or without this patch, but fails on Windows+VisualStudio without this patch.

Reviewed By: sammccall

Differential Revision: https://reviews.llvm.org/D115959