* 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 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

* migrate code example and doc

* add transformer generate square subsequent mask api

* add dtype for input, update doc, use -np.inf

* add dtype for input, update doc, use -np.inf

* numpy -> paddle in conv. test=develop

functionality provided by `normalize`

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

* 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

* fix pool bug, test=develop

* fix coverage,test=develop

* fix bug, test=develop

Fix conv deepwise bug when in_channels=1.

* fix summary rnn

* fix kl_div bug when input shape is [1] and reduction is batchmean

* fix weight

* fix weight and fix doc

* fix embeeding padding idx

* add UT

* fix interval

* fix typo for interp_v2,test=develop

* align with torch, test=develop

* add area mode, test=develop

* fix bug, test=develop

* format notes, test=develop

* update for converage, test=develop

* fix bilinear, test=develop

* fix bicubic, test=develop

* fix typo, test=develop

* fix coverage, test=develop

* fix helper.input_dtype, test=develop

* polish notes, test=develop

* polish notes, test=develop

* polish notes, test=develop

* fix 2.0api, test=develop

* fix, test=develop