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

[Chuanqi Xu via cfe-commits]

ChuanqiXu9 wrote:

> This PR is part of a series aimed at implementing native support for explicit module builds from the Clang driver.

This is confusing. Since explicit modules is an unrelated term with C++20 modules.

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