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

[Gábor Horváth via cfe-commits]

Xazax-hun wrote:

> Do you happen to know any references to similar work, maybe in CSA?

CSA will also remove dead symbols from the path constraints (which is akin to the flow condition in path-sensitive analysis). But this definitely introduced some challenges, there was a recent discussion about some of the fallouts here: https://discourse.llvm.org/t/keeping-the-extent-symbol-alive/76676 

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