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

[Balazs Benics via cfe-commits]

https://github.com/steakhal commented:

Alright. So we can simply mark all the members private. I was surprised a bit.
LGTM, but remove the TODO comment you fix.

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