[clang] [clang][modules-driver] Add scanner to detect C++20 module presence (PR #145220)

[Chuanqi Xu via cfe-commits]

https://github.com/ChuanqiXu9 requested changes to this pull request.

I still hope we can get a new name. It is important for me to understand if some code may affect C++20 module or not by its name. I feel this can be helpful for other developers too.

https://github.com/llvm/llvm-project/pull/145220