API/OP（sequence_first_step，sequence_last_step，sequence_mask，beam_search，beam_search_decode） error message enhancement ,test=release/1.8 (#24668)

* API(dynamic_gru, chunk_eval, BeamSearchDecoder) error message enhancement (#24513)

* dynamic_gru err_msg enhancement, test=develop

* chunk_eval err_msg enhancement and fix crf_decoding output type, test=develop

* BeamSearchDecoder err msg enhancement, test=develop

* API/OP(sequence_expand_as) error message enhancement (#23712) 
Co-authored-by: NGuo Sheng <whucsgs@163.com>

* update err msg for dynamic_lstm and dynamic_lstmp, test=develop

* Fix error info (#23891)

* fix error info for rnn related api

* passed local test, test=develop

* double check the code

* double check the code, test=develop

* update 'shape' check in RNNCell, test=develop

* add long dtype to RNNCell

* fix long type in python3
Co-authored-by: NXingWu01 <wuxing@iie.ac.cn>

* fix rnn check_type list error (#24346)

* fix rnn check_type list error

* tigger ci, test=release/1.8

* update modify, test=release/1.8
Co-authored-by: NXingWu01 <wuxing@iie.ac.cn>

* Add support for dynamic_decode(while) training. test=develop

* Fix assign_op and tensor_array_read_write_op after solving conflict. test=develop

* Fix test_rnn_decode_api.py. test=develop

* Refine docs for apis in rnn.py. test=develop

* Adjust outputs of dynamic_decode. test=develop

* Remove the force_cpu update in assign_op. test=develop

* Remove the force_cpu update in assign_op. test=develop

* Make RNNCell.get_initial_states support batch_dim_idx argument. test=develop

* Rename _create_array_outof_while as _create_array_out_of_while in rnn.py.
test=develop

* split some APIs from nn.py to rnn.py

* split some APIs from nn.py to sequence_lod.py

test=develop

* fix unit-test bug

test=develop

* fix test_layers unit-test bug

test=develop