add __all__=[] to python files not in API public list; import * only support in API public list files (#32643)

* update 2.0 public api in nn

* replace Chinese character cause error in ci;synchronization with pr:#32588 to avoid 'ascii' codec in python2

* numbers used in paddle.nn.functional.norm but not imported

* add norm_by_times param to ctc_loss

* fix doc,test=develop

* add deprecated for softmax_with_cross_entropy, test=develop

* test for deprecated in english doc, test=develop

* test deprecated for softmax_with_cross_entropy in english doc, test=develop

* fix readme and English doc for cross_entropy, test=develop

* rm test for softmax_with_cross_entropy deprecated, test=develop

* update readme for CrossEntropyLoss, test=develop

* fix readme format, test=develop

* fix readme format, test=develop

* fix readme format for cross_entropy, test=develop

* add softmax_switch and fix softlabel for cross_entropy, test=develop

* 1)recovery softmax_with_cross_entropy in fluid 2) change softmax_switch to use_softmax 3) add example for softlabel for cross_entropy, test=develop

* fix Example number for cross_entropy, test=develop

* fix code format, test=develop

* fix for CI-Coverage, test=develop

* fix for CI-Coverage, test=develop

* fix ci-coverage for Non-ASCII character '\xe2' in file, test=develop

* fix ci-coverage for Non-ASCII character '\xe2' in nn.layer.loss.py, test=develop

* update description for doc when use_softmax=Fasle, test=develop

* fix some docs and code example for cross_entropy, test=develop

* delete redundant description for soft_label parameter of cross_entropy, test=develop

* fix some comment for test_cross_entropy_loss.py, test=develop

* fix code bugs

* fix code bugs test=document_fix

* fix code bugs test=document_fix

* fix nll_loss doc;test=document_fix;

* remove numpy and set_device;test=document_fix;

* remove numpy;test=document_fix;

* fix doc example, test=develop, test=document_fix

Fix ops doc for some ops 

* save one name in cross_entropy and softmax_cross_entropy, test=develop

* change used function in CrossEntropy from softmax_cross_entropy to cross_entropy, test=develop

* add soft_label and axis for CrossEntropyLoss and improve performance,test=develop

* fix conflict in nn/functional/loss.py, test=develop

* upgrade comment string to raw string

* fix string in

* fix string with ' '

* revert update on comments

* upgrade only necessary

* fix sample code checker

* fix comments with '''

* refine doc of bernoulli

* fix some problems

* fix unsqueeze

* fix squeeze

* fix doc

* fix English doc for dice_loss, log_loss, unfold and NLLLoss API test=document_fix

also fix `no_grad` alias

modified sample code of CTCLoss & ctc_loss by remove disable_static() & print([.*].numpy()) & alias, test=document_fix (#28403)

* 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 summary rnn

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

fix doc, use to_tensor for the loss ops

* fix bug

* add version check

* fix docs, test=document_fix

* fix formula, test=document_fix

* add binary cross entropy with logit loss

* add functional ctc_loss and CTCLoss class.

* modified docstring of ctc_loss and CTCLoss

* add cross_entropy to nn/layer and nn/functional, test=develop

* use functional/cross_entropy in layer/CrossEntropy

* use functional/cross_entropy in layer/CrossEntropy, test=develop

Fix the API of bce loss and add functional API binary_cross_entropy 

add nn.functional.normalize API for API2.0, fix L1Loss API typo, test=develop

* upate the target to label, test=develop

* Update the code for the margin_ranking_loss, test=develop

* add Class KLDivLoss and function kl_div

add the api and doc for the margin_ranking_loss and MarginRankingLoss

* add nll loss API, update demo code of the comment

fix paddle.nn.loss.L1Loss OP, add paddle.nn.functional.l1_loss OP for API2.0

* add alias in paddle.nn and paddle.tensor test=develop

* add alias in paddle.nn and paddle.tensor dir test=develop

* fix same conflict manually test=develop

* update fc and dygraph alias test=develop

* fix initalizer.py typo test=develop

* fix bug of cross_entropy_loss,test=develop
* fix log_softmax and some comment,test=develop