* fix model bugs, inputs can be InputSpec instance

* correct error message

* Add double grad in Squeeze and Unsqueeze

* Add double grad in Squeeze and Unsqueeze

Add xpu kernel for KUNLUN core:

* accuracy op
* sign op
* scale op
* sum op

Add default atol in xpu unittest.

* Add test attribute in channelwise_quant op, test=develop

* replace config by kwargs

* change save path form dir to prefix

* fix failed unittests

* revert unittest name change

* polish en docs

* add more tests for coverage

* 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

* fix dynamic parallel for hapi

* fix code style

Fix cross, cumsum op docs

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

* keep summary mode unchange

* add no grad decorator

* fix bilateral bug

* modify doc for ParameterList and LayerList, test=develop

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