[clang] [libclang] Replace createRef with createDup (PR #126683)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman requested changes to this pull request.

Requesting changes just to be sure none of the changes from `createRef()` to `createDup()` would have generated a `StringRef` holding a null pointer. I'd be surprised if they did, but a second set of eyes would be helpful.

https://github.com/llvm/llvm-project/pull/126683