[clang] [clang][CodeGen] Make `UnqualPtrTy` truly unqualified (PR #94388)

[Alex Voicu via cfe-commits]

AlexVlx wrote:

> And I still strongly urge renaming what this is, given it is _not_ the type for an unqualified C `void *`, as one would normally expect given it's in Clang. Perhaps DummyPtrTy?

DummyPtrTy seems mnemonic / on point, but it might trigger antibodies from the LLVM side:) Perhaps `NoAddrSpacePtrTy` or something to that extent? What makes this unqualified is it being just a `ptr` and not a `ptr addrspace(n)`. On the other hand, since today it's an unconditional alias for `ptr addrspace(0)`, perhaps `AS0PtrTy` or somesuch thing could also work?

https://github.com/llvm/llvm-project/pull/94388