[clang] [analyzer] Fix "sprintf" parameter modeling in CStringChecker (PR #74345)

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https://github.com/DonatNagyE approved this pull request.

Reasonable semi-automatic refactoring + a small change to fix a nasty crash. It's good to see that you separated the NFC and the bugfix into two commits, it'll make the git history nicer.

It's a bit unfortunate that there are many locations where `CE` is replaced by the more verbose `Call.getOriginExpr()`, but I guess that's the price of this improvement.

https://github.com/llvm/llvm-project/pull/74345