Move OpInfo class into new opinfo folder (#82540)
Ref #82518
Starting small to minimize merge conflicts, this moves the top-level
class definitions and some helper functions into the `opinfos` folder.
It also brings `common_methods_invocations.py` to just below 1MB.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/82540
Approved by: https://github.com/albanD
