Rename boxing/unboxing files and utilities (#35411)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/35411
The file and class names in ATen/core/boxing were quite confusing.
Let's rename them for readability.
Also move function schema inference out of the boxing logic into op_registration.h where it belongs.
ghstack-source-id: 101539206
Test Plan: waitforsandcastle
Differential Revision: D20653621
fbshipit-source-id: 6a79c73d5758bee1e072d543c030913b18a69c7c
