[jit] Enable IValue to hold a PyObject (#32491)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/32491
This PR enables IValue to be able to hold a pure PyObject by adding a
new enum tag, a new jit_type to denote PyObject existance in IValue and
the JIT type system. We don't and not plan to expose this to user.
This is the basic piece that enable ivalue to be adopted broader like
making RRef always hold IValue, it might also simplify some compiler
logic
ghstack-source-id: 97039980
Test Plan: Imported from OSS
Differential Revision: D19502234
fbshipit-source-id: 90be001706d707d376cfbea25980fd82980df84a
