[clang] [NFCI][analyzer] Regularize NodeBuilder classes (PR #180960)

[Donát Nagy via cfe-commits]

NagyDonat wrote:

@steakhal By the way, now that you highlighted the question of polymorphism and virtualization, I realized that there is no actually useful polymorphism within the `NodeBuilder` class hierarcy. I will create a commit that removes all of this.

https://github.com/llvm/llvm-project/pull/180960