* 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)

test=develop

- compilation fix

test=develop

API(lstm_unit, lstmp, sequence_mask, sequence_enumerate, sequence_conv) error message enhancement (#27572)

* API(Compute) error message enhancement on line 44, 50, 53.

* lstm_unit error message enhancement.
lstmp error message enhancement.
sequence_conv error message enhencement.
sequence_enumerate error message enhencement.
sequence_mask error message enhencement.

* Update lstm_unit_op.cc

* Update lstm_unit_op.h

* error msg enhancement.

* Update sequence_conv_op.cc

* Update lstm_unit_op.cc

* Update sequence_conv_op.cc

* Update sequence_enumerate_op.cc

* Update sequence_enumerate_op.cu

* Update sequence_enumerate_op.h

* Update sequence_pool_op.h

* error message enhencement.

* error message enhancement.

* Optimize the error message for OPs.

* Optimize the error message for OPs in details.

* 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

* modify doc for Layer, test=develop

* modify doc for Layer2, test=develop

* set dtype default value to float32, test=develop

* add example code for paddle.nn.Layer, test=develop

* set create_parameter and create_variable dtype default value to None, test=develop

* modify some example code, tet=develop

* refine, test=develop

* del no ues code, test=develop

* modify doc, example code, args, test=develop

* modify doc, test=develop