Run test_functional_api.py with both legacy and native funcol impls (#119982)
Additional changes: tests in test_functional_api.py uses multi-threaded pg which is implemented in Python. For the native ops to call into the Python pg implementation, glue code in PyProcessGroup is required for each collective. This PR also adds a few pieces of previously missing glue code, which are necessary for running test_functional_api.py with native funcol.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/119982
Approved by: https://github.com/wanchaol
