Reapply "c10d: add Collectives abstraction (#125978)" (#126695)

This reverts commit d9c3485146913324ab4b3e211d2a4517e138f4af.

Reapplies #125978.

Pull Request resolved: https://github.com/pytorch/pytorch/pull/126695
Approved by: https://github.com/c-p-i-o

torch/distributed/__init__.py

@@ -54,6 +54,8 @@ if is_available():
         set_debug_level,
         set_debug_level_from_env,
         _make_nccl_premul_sum,
+        _ControlCollectives,
+        _StoreCollectives,
     )
 
     class _DistributedPdb(pdb.Pdb):