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

[Michael Spencer via cfe-commits]

https://github.com/Bigcheese approved this pull request.

With the last bit this looks fine to me, but you should wait for Chuanqi and see if the naming should be changed.

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