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

[Donát Nagy via cfe-commits]

https://github.com/NagyDonat commented:

I strongly support the idea that we should eventually represent the memory space of a memory region by a state trait (instead of the "fake" super-region) and I am grateful that you're working on this.

I added a few suggestions in inline comments that could simplify the logic and ensure better behavior w.r.t. element and field subregions. (Also there are a few trivial nitpicks about comments.)

In my opinion it would be nice to have some code path that sets and uses these MemSpace traits (even in this initial commit), because that would let us test the code and verify that it's working correctly.

However, I'm not totally opposed to accepting this as an NFC (no functional change) commit, but in that case, please add `[NFC]` to the review/commit title (before merging the commit) as that helps developers who want to quickly find a commit which is responsible for a certain issue. 

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