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

[Alex Trotta via llvm-commits]

Ahajha wrote:

Does `nb::sig` work? It completely replaces the type signature, which might be clunky, but it's an option and doesn't involve a separate file.

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