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

[Ingo Müller via llvm-commits]

https://github.com/ingomueller-net approved this pull request.

I am generally supportive as I think this is very valuable but my CMake expertise is too limited to give useful feedback.

OoC: How many of the bound functions need a manual `nb::sig` and why? How will author authors know when to add it and whether what they do works?

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