[clang] [analyzer] Enforce not making overly complicated symbols (PR #144327)

[Donát Nagy via cfe-commits]

https://github.com/NagyDonat commented:

Thanks @haoNoQ for this great idea and @balazs-benics-sonarsource for the quick implementation!

I'm completely satisfied with the current direction of development on this PR -- using this fresh symbol type instead of `Unknown`s and `nullopt`s and early returns addresses my concerns about code complexity issues.

https://github.com/llvm/llvm-project/pull/144327