[clang] [clang][dataflow] Model conditional operator correctly. (PR #89213)

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martinboehme wrote:

Needed to revert this because it turns out that, embarrassingly, I was locally running my tests in `Release` mode, i.e. with `assert()` disabled. I'm working on a PR to re-land this that fixes the assertion failures that were occurring.

https://github.com/llvm/llvm-project/pull/89213