[clang] Reapply "[C++20][Modules] Implement P1857R3 Modules Dependency Discovery" (PR #173130)

[Corentin Jabot via cfe-commits]

https://github.com/cor3ntin approved this pull request.

@yronglin you can land the PR but please monitor the bots and revert as needed. if you cannot watch over the bots, do not land the pr until you can :)

https://github.com/llvm/llvm-project/pull/173130