[llvm] [mlir] [MLIR][Python] reland (narrower) type stub generation (PR #157930)

[Jacques Pienaar via llvm-commits]

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

Overall looks good, I didn't verify all the types returned (sigs), I assume there would be errors reported if they didn't match. That being said, would it make sense to diff the previously checked in vs generated?

https://github.com/llvm/llvm-project/pull/157930