[clang] [analyzer][NFC] Introduce APSIntPtr, a safe wrapper of APSInt (1/4) (PR #120435)

[Gábor Horváth via cfe-commits]

Xazax-hun wrote:

I see that `unsafeConstructor` is used in the follow-up PRs. I'd move the addition of that function to the first PR that is using it. 

https://github.com/llvm/llvm-project/pull/120435