* Rewrite unit test for unified allreduce op. Removing the legacy unit test.
* Revise formats, fusion_op bindings. Put all tensors as optional inputs.
* Move the MoeAllreduceOp to a separate custom op.
* Move all the fusion patterns to the new version of the AllReduce fusion kernel. Remove the AllReduce strategy config. Revise the AllReduce strategies and fusion pattern definitions.
* Add more TODOs, fixing minor bugs, and remove legacy code.
Signed-off-by: Yukun He <23156053+hyukn@users.noreply.github.com>