[clang] [analyzer] Turn NodeBuilderContext into a class (PR #84638)

[Balazs Benics via cfe-commits]

steakhal wrote:

Thanks for the PR.
I think it would make sense to not expose data members in a class' public api.
We might need some member functions along the way to make this possible.

https://github.com/llvm/llvm-project/pull/84638