Differential Revision: D63206258
This diff introduces a mechanism to generate a json-compatible deserializer in cpp using nlohmann json (already being used by AOTI).
Why we need this? Because there will be a lot of cases where people don't want to use Python to load the graph (e.g. cpp runtime), and instead they can use this header to deserialize the JSON graph.
Every time we call update_schema.py to update the schema, the header will be auto generated and included into the source files.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/136398
Approved by: https://github.com/angelayi
