* update assign/cast/linspace/addcmul op doc for 2.0 api,test=document_fix

* fix bug about cast doc for 2.0 api,test=document_fix

* fix norm api doc, test=develop

* fix error message, test=develop

* fix api norm, test=develop

* add adagrad, test=develop

* fix bug, test=develop

* fix bug, test=develop

* add spetral_norm, test=develop

* fix adagrad, test=develop

* merge , test=develop

* 1. remove paddle.unique_with_counts api, which counts as unique api
2. add paddle.math.increment(x, value=1.0, name=None) api
3. replace paddle.sums with paddle.add_n api
4. update paddle.metric.accuracy api (add name parameter)

Update code examples for api2.0 

As the title

* refine parameters order && doc

* update rmsprop doc

* refine adam/transpose/unstack/stride_slice

* fix bug && doc

* fix doc

* bug fix

* bug fix

* fix doc

* fix doc

* fix doc

* fix doc

* depercate old strided_slice

* update doc

* set default value for name

* update doc

* add flattern weight of lstm

* 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

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

* refine grid_sample and temporal_shift

* update 2.0 API for dice_loss and log_loss test=document_fix

* fix the scatternd/scatterndadd

* fix the doc of scatter

* replace rank with ndim

* migrate code example and doc

This PR fixed two bugs when converting LSTM in dy2stat:

is_unsupported has a condition can trigger Python syntax error
LSTM API's implementation in _rnn_static_graph doesn't include parameter initialization, which can cause dy2stat error.

* fix is_empty api and code example; test=develop

* remove inplace argument

* fix sample code

* fix sample code

1. fix a bug that paddle.nn.RNN does not initialize the state for the cell correctly;
2. add unittest for paddle.nn.RNN and paddle.nn.BiRNN

* modified sample code of add_position_encoding to  2.0, test=document_fix

* use core.op in add_position_encoding API.

* add test for add_position_encoding in dygraph mode

* fix example code

* rename var to tensor

* remove static

* fix return type

* add float64 input to ctc_loss

* modified error message of  warpctc

* update repo and tag of warpctc

* add test for warpctc with float64 input

* modified warpctc.cmake to make sure build always

* resolved sample code bug of warpctc

* add core.ops in warpctc dygraph

* fix a bug of test

* Fix example code of api `fluid.layers.switch_case` to use api2.0

* delete `paddle.nn.switch_case` alias and add `paddle.static.nn.switch_case`

* Fix example code of api fluid.layers.case

* delete paddle.nn.case alias and add paddle.static.nn.case

* add static check on data()

* follow comments

* fix ut

* Makes the Bind Method more intelligent

* Makes the Bind Method more intelligent

* fix unittest

* fix unittest

* fix conflict

* add double grad compute for batch norm,test=develop

* fix unittest, test=develop

* remove unuse tensor,test=develop

* add format,test=develop

* update, test=develop

and optimize the c++ implmentation of empty op as PR#26659 reviews,
and add bool for shape op.