[clang] [Clang] Implement P3034R1 Module Declarations Shouldn’t be Macros (PR #90574)

[via cfe-commits]

https://github.com/cor3ntin commented:

I think this is starting to look pretty good.

Can we simplify further by lexing the partition along with the module name, when there is one? 
We could also have a ModuleNameInfo::toString() function we could use in a couple places.

https://github.com/llvm/llvm-project/pull/90574