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

[Gábor Horváth via cfe-commits]

https://github.com/Xazax-hun commented:

I did not do a deep review yet but the approach looks reasonable to me after quickly skimming this. Will try to get back to this soon. 

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