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

[Michael Flanders via cfe-commits]

Flandini wrote:

> I like the direction of this PR but at the same time it makes memspaces a bit more error prone to use. Do you think we could find a way to prevent using `isa` on memspaces?

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? IIUC, from previous chat with @steakhal, the eventual goal is to get rid of the MemSpaceRegion part of the MemRegion class hierarchy and replace it with something else. 

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