move some codegen utilities into utils.py (#63094)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/63094
This PR:
- Moves `FileManager` and its dependencies (`assert_never` and other imports) to `utils.py`, and updates all of the call-sites with the fresh imports
- Passes the list of NativeFunction objects into `gen_trace_type` directly, instead of requiring the function to regenerate it (we already have it)
The purpose of the reshuffling is to avoid circular dependencies in the next PR, where I add codegen for the functionalization pass, which gets called from `gen.py` (but depends on some stuff from the autograd codegen - in partulcar, the list of view ops).
Test Plan: Imported from OSS
Reviewed By: albanD
Differential Revision: D31942096
Pulled By: bdhirsh
fbshipit-source-id: 36118facae61f25f8922bb43ad2818c80b53504e
