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

[Maksim Levental via llvm-commits]

makslevental wrote:

> Right, but can't we match `.*` (with no other effects) and add a few `\from` imports for basically every method? I haven't tested and won't be offended if you don't want to; just throwing around random thoughts... 😉

Lol you could but the missing imports aren't the real issue here - without explicit `nb::sig` (or using `Py*` types) what you get in the stub is stuff like `MlirType`, `MlirValue`, etc. Don't worry I'm well on my way to converting to `Py*` types as we speak 😄.

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