[FSDP2][ez] Combined communication test files (#120904)
This just combines the unit tests for the collectives ops for copy-in/all-gather/copy-out and copy-in/reduce-scatter/view-out with the unit tests for communication schedule. I was mainly thinking to try to not have too many test files.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/120904
Approved by: https://github.com/Skylion007, https://github.com/wanchaol
ghstack dependencies: #120659
