[clang] [NFC][analyzer] Refactor Environment to map Expr to SVal instead of Stmt to SVal (PR #193295)

[Balázs Benics via cfe-commits]

https://github.com/steakhal commented:

I believe you should benchmark this @NagyDonat 

If no report differences appear, then I'll approve and merge this.

https://github.com/llvm/llvm-project/pull/193295