[clang] [ObjC] Sort constant NSDictionary keys by UTF-16 code unit (PR #209927)

[Adam Cmiel via cfe-commits]

AdamCmiel wrote:

@ahatanak rebased onto current main (now a9fe0297, no conflicts) — both of your Aug 14 threads are addressed in the top commit: UTF-8 byte-order sort under -fno-constant-cfstrings, and the truncation warning skipped there, each with a test. Could you take another look when you get a chance?

https://github.com/llvm/llvm-project/pull/209927