[clang] [clang][dataflow] Manage stacks of formulas directly instead of recur… (PR #175980)

[Yitzhak Mandelbaum via cfe-commits]

https://github.com/ymand approved this pull request.

Thanks!

Fun note (which I don't recommend for this PR, but thought you might appreciate): if you want to drop the special-case logic for the empty stack, you can add a new (special) unary operation representing a complete formula and push that onto the stack to start the process. Then, the empty stack means that you're done (and I think can become the loop condition?). This corresponds to the special "start" symbol that you typically find in textbook treatments of grammars.

https://github.com/llvm/llvm-project/pull/175980