[clang] [nfc][analyzer] Add MemSpace trait to program state (PR #123003)

[Gábor Horváth via cfe-commits]

Xazax-hun wrote:

> Do you mean moving away from a class hierarchy definition for memspaces and towards something else, maybe a enum Kind definition, or maybe just try to hide all the casting behind a different API?

I think it would be nice to do the latter in this patch so using `isa` directly will lead to a compilation error, would prevent some potential errors. We could do the former as a follow-up later. 

https://github.com/llvm/llvm-project/pull/123003