[llvm] [Support] Introduce formatv variant of createStringError (PR #80493)

[Fangrui Song via llvm-commits]

https://github.com/MaskRay approved this pull request.

Thanks for the PR. This helps avoid the dangerous `llvm::format`.

I left a comment on https://discourse.llvm.org/t/llvm-format-is-dangerous/71994/16?u=maskray so that more folks are ware of this PR. This LGTM but it should wait a bit seeking more opinions.

https://github.com/llvm/llvm-project/pull/80493