* support process group in dp with fleet api

* update

* fix uts

* update

* add reducer

* add tensor_indices in AssignGroupBySize

* add rebuild group in reducer

* add reducer

* refine envent for memorycopy

* add concat&split for allreduce

* apply concat & split for fuse tensor

* fix nccl dep

* fix the untest, compile problem and ddp initialize problem

* fix untest for mac & add some comments & solve the repeated param in sublayers

* fix untest for windows & fix document