[JIT] Allow registering Decompositions
- Allow registering custom decompositions
- Add easier API for invoking decompositions
- Shorten API names (no users yet)
I am doing these as one pr because they are fairly short/simple and because github first does not support ghstack yet.
cc @Chillee @zou3519
Pull Request resolved: https://github.com/pytorch/pytorch/pull/76252
Approved by: https://github.com/davidberard98
