* add matmul doublegrad op

* fix compile errors

* modify code according to review

* delete float16

* Reimplement paddle.static.nn.fc, mainly change the parameters and English documentation.

* Polish the documentation format.

* disable_fuse_all_reduce

* fix test

* fix ut

* fix pool3d bug, test=develop

* fix unitest, test=develop

* fix test and fix pool2d bug, test=develop

* Add api of constant in paddle.nn.initializer

* Add api of constant in paddle.nn.initializer

* Add api of constant in paddle.nn.initializer

* Add api of constant in paddle.nn.initializer

* Add api of constant in paddle.nn.initializer

* Add api of constant in paddle.nn.initializer

* Add api of constant in paddle.nn.initializer

Polish the english documentation and example of paddle.nn.Linear and paddle.nn.functional.linear (#27759)

* reimplement paddle.nn.functional.sigmoid_focal_loss. test=develop

* fix reduction error message. test=develop

* fix exp. test=develop

* reset the shape of logit. test=develop

* delete disable_static in example. test=develop

* fix bilateral bug

* modify doc for ParameterList and LayerList, test=develop

* add empty line after code-block, test=develop

* modify doc for Layer, test=develop

* modify doc for Layer2, test=develop

* set dtype default value to float32, test=develop

* add example code for paddle.nn.Layer, test=develop

* set create_parameter and create_variable dtype default value to None, test=develop

* modify some example code, tet=develop

* refine, test=develop

* del no ues code, test=develop

* modify doc, example code, args, test=develop

* modify doc, test=develop

* fix huber_loss ans npair_loss doc and example code, test=document_fix

* remove disable_static in example code, test=document_fix

* remove huber_loss and refine npair_loss example code, test=document_fix

* remove huber_loss in functional/__init__.py, test=document_fix

Add Simnet Test for V2 APIs.

We used tool from https://www.paddlepaddle.org.cn/documentation/docs/zh/2.0-beta/guides/migration_cn.html#paddle1-xpaddle2-0beta to do v1.x to v2 transformation.

This PR pulled changes from #27430, please DO NOT merge before #27430 is merged

* Add test skip from cmake

* Remove print

* Add avx instructions check

* Small fix

* Change function name

* Change uint to unsigned int

* Fix ErrorClipByValue api and demo code of clip_by_value. test=develop
Co-authored-by: Ntianshuo78520a <707759223@qq.com>

* test=develop, update example

* move dygraph amp api to paddle

* refine code and add unit test

* add multinomial cpu kernel

* fix C++ notype error

* fix windows ci array len error

* let array len be const

* change array to vector

* add cuda kernrl with num_distribution is 1, and not support replacement=False

* add multinomial python api

* support num_distribution different multinomial distributions

* add categorical class

* fix test_distribution enable_static error

* add unittest for different setting of Categorical

* optimize format

* little change

* little change

* add raise error if shape not match, optimize format

* fix windows CI dtype error in concat

* little changes

* little changes2

* change values type to int64

* change values type to int64

* change values type to int64

* Add test_resnet_v2.py test=develop

* refine grid_sample and temporal_shift

* fleet support non_distributed training in dygraph mode; test=develop