[feature] Add PyO3 integration for ast-grep

[HerringtonDarkholme]

We only have napi integration for nodeJS. Supporting Python community is a good idea!

https://github.com/PyO3/pyo3 looks like a good library for this.

• Support SgNode methods on par with Napi
  • field
  • parent
  • child
  • ancesrots
  • next
  • next_all #681
  • prev
  • prev_all
• [pyo3] Implement directory based file traversal (a.k.a napi's findInFiles) #699
  • parse_files
  • find_in_files
• Implement better runtime properties of SgNode via magic methods
  • __hash__
  • __eq__
  • __str__
  • __repr__
  • __get_item__ for access single meta-variable without None assertion
• Implement better typing info for Python users
  • config
  • rule
  • SgNode
  • SgRoot
  • Range/Pos
• Error Handling

[HerringtonDarkholme]

Implementation note:
We can use Py<T> to represent the Python managed ast-grep root.
See https://pyo3.rs/v0.12.3/types.html?highlight=Py#pyt-and-pyobject

First, we need to have a PyRoot

struct PyRoot {
  root: Root,
}

Secondly, we need to add definition of Node. The node

struct PyNode {
  node: Node<'static>,
  root_ref: Py<PyRoot>,
}

The crux here is that Node's lifetime is 'static, meaning the node is also managed by Python garbage collector.
The root_ref increments the PyRoot's ref_count so it will not be gc-ed if PyRoot is not referenced directly but still referenced by PyNode (It's ugly and expose low-level details. I prefer napi's sharedReference abstraction)

Finally we need GIL to get a reference of PyNode, this will involve some lifetime cast.

[HerringtonDarkholme]

Closed!