SDK Integration 1/n: AOT DDI Serialization (#3957)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/3957

**See [design doc](https://docs.google.com/document/d/1KQ0vH0IhZK24sBbym7TYXfYssAgtPjI-htcxraoxEaM/edit).**
__1/n: AOT DDI Serialization__
- I begin by modifying `OperatorCall`'s flatbuffer schema to have `node_id`, which will store the DDI
- I pass optional `DelegateMappingBuilder` to `VkGraphBuilder`'s Python ctor and then assign and construct `OperatorCall` objects with generated DDIs
- I modify the `OperatorCall` Python dataclass to have `node_id` as well
ghstack-source-id: 229958489
exported-using-ghexport

Reviewed By: SS-JIA

Differential Revision: D57424318

fbshipit-source-id: a77e9a78ebb2482342169d60adde4325fef81669