[clang] [clang] Add separate C++23 extension flag for attrs on lambda (PR #74553)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

Changes LGTM but we should probably document this extension at this point. Can you add this to the table at: https://github.com/llvm/llvm-project/blob/546a9ce80cac8fe73d239496010ae84972da3ca8/clang/docs/LanguageExtensions.rst?plain=1#L1455

https://github.com/llvm/llvm-project/pull/74553