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

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

Can you make sure that at every place this PR touches `const` makes sense? I found out recently that we can be quite good at pretending that something is `const`, all the way down until we realize we need a `const_cast`, because modification is required in that one place.

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