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

[Mehdi Amini via llvm-commits]

joker-eph wrote:

> Note you can do so with something like [...]

FYI, in general I test PR that way:
```
$ git fetch origin pull/157853/head
$ git checkout FETCH_HEAD
```

I checked and locally I see still the standalone example being broken: 

```
# | 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
```



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