* support control flow

* supoort sync_parameters_buffers

* fix the bug of sparse embedding

* upgrade vlog

* train from dataset fetch optimize

* new group

* ci compatible fix

* assert nccl

* update, test=develop

* update, test=develop

* fix zip py3 bug

* add 1f1b scheduler for pp, test=develop

* fix one ps gradient clip

* remove the send/recv of tensor size, but users have to specify the shape of the received var explicitly.

[Kunlun]Multi xpu dygraph performance optimization , add distributed.spawn support for multi xpu and some bug-fixes (#31130)

* topo and memory performance for heterps; test=develop
* add trainwithprofiler in heter trainier; test=develop

* update, test=develop

* fix entry

* fix distributed lookup table fuse case

* fix entry bug at first time

* move entry from paddle.fluid -> paddle.distributed

* fix ut with paddle.enable_static()
Co-authored-by: Nmalin10 <malin10@baidu.com>

* test=develop, save/load, shrink
Co-authored-by: NseiriosPlus <tangwei12@baidu.com>

* Fix the bug in fleet amp_init.

* Fix the amp_init unit test.

* add fleet amp.init()

* add unittest for fleet_amp_init

* update, test=develop

* add trainers for pserver

Change-Id: I1a75793ec81ce126d07f4c47cae09b95d530bbc8

* test=develop, fix fleet.metrics(mse, rmse, mae)

Co-authored-by: NseiriosPlus <tangwei12@baidu.com>

* test=develop, add distributed_infer

* rename sendrecv.proto to namespace paddle.distributed

* split ps with distributed

* add save tensor support
Co-authored-by: NseiriosPlus <tangwei12@baidu.com>

* add tensor table

* Simplify the options of spawn based on fleetrun

* polish details

* polish doc details

* set flags_selectedd_gpus for spawn

* add cond for unittest

* Delete test_no_single_process_using_multi_gpus_in_spawn.py

* Update spawn.py

* Update nccl_context.cc