[clang] [clang][Sema] Deprecate `global`/`unknown` in `lifetime_capture_by` (PR #196635)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

This is still marked as a draft but seems ready for review?

The changes should also come with a release note in `clang/docs/ReleaseNotes.rst`.

https://github.com/llvm/llvm-project/pull/196635