* Add pure fp16 training with master weights. (#27712)

* add the weight decay func for the momentum op

* Add the multi_precision function in Momentum Optimizer.

* Make sure that the initial value of master weights are same with the fp16 weights.

* add static loss scaling.

* add the rescale_grad function in the pure fp16 training.

* use the original momentum updating method.

* Polish some codes, such as variable names.

* add docstring for apis.

* update the var creation details of _create_master_weight.

* not modify codes about imperative momentum updating.

* Fix the error of test_dist_sparse_tensor_load_momentum UT.

* add unit test for multi precision fp16 training.

* add more unit tests for CI.

* Use lower threshold values for allclose comparing in test_multi_precision_fp16_train UT.

* add complex64 and complex128 type; add +-*/@ and slice opreator for complex types

* add test cases for complex elementwise, matmul and getitem unittest

* add test cases for complex types

* add test cases for complex matmul unittest

- Make sure that oneDNN memory descriptors are created only once at
first iteration.

* fix paramete prefetch & device guard
Co-authored-by: NMrChengmo <cmchengmo@163.com>
Co-authored-by: Nchengmo <chengmo@baidu.com>

* test=develop, optimize async prefetch

fix gru gcc7.4 bug for the gru compile

update expand as op to use the shape of the target tensor instead of the target tensor itself. (#29020)

* update, test=develop

Add eigen gru and fix the dropout bug in the rnn 

* remove -DSUPPORTS_CUDA_FP16 in cuda.cmake

* comile with cuda9

* add some unittest

* notest;test=coverage

* add unittest for trt plugin swish && split

* update ernie unittest

* fix some error message

* remove repeated judgement of CUDA version in mbEltwiseLayerNormOpConverter

* fix comile errror when CUDA_ARCH_NAME < Pascal"

* fix comile error

* update unittest timeout

* compile with cuda9

* update error msg

* fix code style

* add some comments

* add define IF_CUDA_ARCH_SUPPORT_FP16

* rename IF_CUDA_ARCH_SUPPORT_FP16 to CUDA_ARCH_FP16_SUPPORTED

Fix ops doc for some ops 

* Add bf16 pool2d and unify bf16 unit tests

* Add change default ops test

add uint8 for reshape operator

Simple code clean up

remove eigen threadpool for the speed up

* test=develop, optimize global_step

* refactor momentum op to combine weight_decay (scale op and sum op)

Adding uint8 support for squeeze operator.

* Add bf16 matmul, fc, elementwise add and mul

* Correct unit test

* 1.add xpu slice op 2. add xpu top_k op 3.modify xpu cast to new api

* 1.add xpu slice op 2. add xpu top_k op 3.modify xpu cast to new api

* add lstm, simple rnn op kernel

* fix the test_lstm for the rnn op

* change func name

* fix forward postprocess bug

* add gru forward, backward code

* remove unittest.skipIf; use a big rnn op instead of combination op

* fix input doesn't have gradient bug

* add eigen lstm forward, backward
Co-authored-by: Nwawltor <fangzeyang0904@hotmail.com>

* adjust kunlun header file
*test=kunlun

* update kunlun unittest
*test=kunlun

* update xpu unitest
* test = kunlun

* update xpu unittest
* test=kunlun

* update xpu unitest
* test=kunlun

* Add multi_gru op and tests

* removed redundant disable_dygraph()

Add new operator log10

test=develop