remove fluid.initializer.UniformInitializer, ConstantInitializer, NormalInitializer, TruncatedNormalInitializer, XavierInitializer, BilinearInitializer, MSRAInitializer, NumpyArrayInitializer and calculate_gain.. (#49498)

* move UniformInitializer and ConstantInitializer

* more modify

* circular import resolved

* another circular import resolved?

* more circular import 2

* circular import 3

* change import paddle in metric.py

* BuildStrategy import from fluid

* modify the framework import path in common.py

* change rnn.py import, from static to original framework

* change import static in the nn folder

* default_main_program should import from common_ops_import

* add import paddle in param_attr.py

* use core not paddle module for using VarDesc

* another old uniform

* mistake that use Uniform instead of UniformInitializer

* modify UniformInitializer doc

* move fluid.NormalInitializer to nn.initializer.NormalInitializer

* remove import of Normal in fluid.layers.nn.py

* remove more import of old Normal

* remove more import of old Normal

* sample code modify and tests modify import

* is_listen_failed passing arg should be log file

* problem solved

* a mistake solved

* comments resoleved and remove paddle.fluid.initializer.TruncatedNormalInitializer

* remove paddle.fluid.initializer.XavierInitializer and paddle.fluid.initializer.MSRAInitializer

* remove paddle.fluid.initializer.BilinearInitializer NumpyArrayInitializer and set_global_initializer

* change fluid to static

* change static to fluid to avoid circular import in distributed_strategy.py

* fix example code and test_initializer

* ValueType

* sample code fix

* change set_global_initializer back to fluid

* put paddle.static.BuildStrategy.ReduceStrategy into the fuction to avoid circular import

* remove calculate_gain, delete BilinearInitializer and revert set_global_initializer

* change the time of using UniformInitializer, ConstantInitializer, NormalInitializer, TruncatedNormalInitializer, XavierInitializer, MSRAInitializer, NumpyArrayInitializer as few as possible

* fix argument incampatible

* fix more arg incompatible

* fix test_prelu_op_xpu.py Constant

* fix inaccurate doc

* more doc fix: default value

* rm retain_grad_flag for tests

* modify transpose op

* retain grads for xpu tests

* lint

* modify xpu test

* [remove fluid] under unittesets

* [remove fluid] under unittesets

* [remove fluid] under unittesets

* [remove fluid] under unittesets

* [remove fluid] under unittesets

* [remove fluid] under unittesets

* [remove fluid] under unittesets

* [remove fluid] under unittesets

* [remove fluid] under unittesets

* [remove fluid] under unittesets

* [remove fluid] under unittesets

* [remove fluid] under unittesets

* [remove fluid] under unittesets

* [remove fluid] under unittesets

* [remove fluid] under unittesets

* [remove fluid] under unittesets

* isort all files

* revert conflicting files

* revert conflicting files

* revert conflicting files

* revert conflicting files

* revert conflicting files

* update config

* re-blacken python code

* temporarily disable date and diff_py_file

* skip a format

* [CodeStyle] remove all future import

* revert test_error.py

* restore future import in example code

* use yapf to format all python file

* yapf exclude two unittests file for they rely on writing and reading file, and format will break them

* disable diff_py_file because too many diff files cause command following failed

* [Eager] FLAGS_retain_grad set false

* Add FLAGS_retain_grad_ for some tests

* Add FLAGS_retain_grad_ to some tests

* modified set_flags

* modified set_flags

* fix windows-ci and windows-openblas-ci

* import paddle.fluid

As the title

* add fake interface for hook in static mode

* add unittests

* fix failed unittests

Refine fake_interface Error Message

Add clone method for static Variable so that this interface will be same as dygraph. It fixed some bugs in dy2stat

[inplace] Add ShareHolderWith for class Variable and SharePlaceholderWith in VarBase.detach() to share the same Tensor/SelectedRows (#29267)

* add decorator, test=develop

* add fake_interface_only, test=develop

* remove some dygraph_not_support, test=develop

* change dygraph to imperative, test=develop

* modify fc to linear in sample code, test=develop

* remove FC, test=develop

* remove warnings, test=develop

* drop fluid/imperative/README.md , test=develop

* change fc to linear, test=develop

* polish code style, test=develop

* test=develop, fix docker with paddle nccl problem

* test=develop, Add Variable api and refine dygraph related API

* test=develop, Add Variable api and refine dygraph related API

* test=develop, refine test for new api and error info

* test=develop, refine error info and test_layers

* test=develop, add API.spec

* test=devleop, fix to_string python2 and python3 compat error and refien doc

* test=devleop, add API spec

* test=devleop, update API spec

* test=devleop, update API spec

* test=develop, invoke ci

* test=develop, fix example code

* test=develop, update API spec

* test=develop, add compat test and fix inplace campat dict error

* add to and detach for Variable in dygraph, test=develop

* add detach for Variable in dygraph, test=develop

* add detach for Variable in dygraph, test=develop

* add detach for Variable in dygraph, test=develop

* add detach for Variable in dygraph, test=develop

* add detach for Variable in dygraph, test=develop

* add exception check, test=develop