[clang] [clang] Adding an API to create a `CXStringSet` from a Vector of `StringRef`s (PR #136773)

[Jan Svoboda via cfe-commits]

https://github.com/jansvoboda11 approved this pull request.

LGTM, thanks! I left a couple of comments for your consideration, but don't feel obligated to incorporate them.

https://github.com/llvm/llvm-project/pull/136773