[clang] [clang] Be const-correct with all uses of `Module *`. (PR #93493)

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

Sounds like you have a plan after this PR, which is good. I was worried that you're just applying `const` where it doesn't cause issues _today_. Such approach to const-correctness has been failing us (it leads to `const_cast`s down the usage chain).

https://github.com/llvm/llvm-project/pull/93493