[llvm] [mlir] [MLIR][Python] reland stubgen (PR #157853)

[Maksim Levental via llvm-commits]

makslevental wrote:

> ```
> # | ninja: error: 'build/tools/mlir/python/type_stubs/_mlir_libs/_mlir/__init__.pyi', needed by 'python_packages/standalone/mlir_standalone/_mlir_libs/_mlir/__init__.pyi', missing and no known rule to make it
> ```

Can you check your nanobind version: `pip freeze | grep nanobind`; I (and others) observed this failure mode due to a non-updated version of nanobind (which dumps the stubs differently).

https://github.com/llvm/llvm-project/pull/157853