[clang] [Clang][analyzer] replace Stmt* with ConstCFGElement in SymbolConjured (reland) (PR #137355)

[Balazs Benics via cfe-commits]

steakhal wrote:

Sorry about my availability. I barely have any focus time these days.
Could you please split your commit into: 1) the original commit we had to later revert, 2) the changes to fix it that would make it on par with what you have here now

This would allow me to review the affected parts, saving me precious time. I know you did a diff of the diffs, but that's not really helpful.

https://github.com/llvm/llvm-project/pull/137355