[clang] Reland [clang][modules-driver] Add scanner to detect C++20 module presence (PR #147630)

[Naveen Seth Hanig via cfe-commits]

naveen-seth wrote:

This now also leverages the `Scanner` in `DependencyDirectivesScanner.cpp` to reuse its logic for properly lexing module related directives. For this to happen, I had to first land two fixes with #148674 and #148685.

https://github.com/llvm/llvm-project/pull/147630