[clang] [clang][analyzer] Bring checker 'alpha.unix.cstring.NotNullTerminated' out of alpha (PR #113899)

[Donát Nagy via cfe-commits]

https://github.com/NagyDonat commented:

Overall I support moving this checker out of alpha, because its narrow functionality indeed seems to be stable enough for general use.

However, eventually it would be good to extend this checker to get a "real" NonNullTerminated checker that can deduce that certain "normal" strings don't have a proper null terminator. 

https://github.com/llvm/llvm-project/pull/113899