[clang] [clang][nullability] Don't discard expression state before end of full-expression. (PR #82611)

[Yitzhak Mandelbaum via cfe-commits]

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

I'm a little concerned with the complexity and cost required to support this optimization. With this added cost, do you know if the analysis still faster (and less SAT timeouts?) than if we just did the simple thing of not dropping state?

https://github.com/llvm/llvm-project/pull/82611