* [cherry-pick]fix bug in reshape: (#20781)

consider the situation that shape of input can contain more than one -1.

* [cherry-pick]support Tensor for split and concat, support -1 in num_or_sections, add check num_or_sections (#20780)

* improve split and concat op:
1. support Tensor for argument 'dim' in split op.
2. support Tensor for argument 'axis' in concat op.
* redefine function GetDataFromTensor and set unknown output shape to - 1.
* add check: Attr(sections) match Input(X).
* support Tensor for attr(sections) and attr(sections) can contain -1.
* modify error message and fix bug for concat and call Resize only when necessary.
test=release/1.6

* [cherry-pick]improve unsqueeze op to support int, Tensor for argument axes (#20824)

* improve unsqueeze op to support int, Tensor and Tensor list for argument axes.
* call Resize only when necessary. test=release/1.6

* [cherry-pick]Compatible int32 and int64 for attr in concat/split/unsqueeze. test=release/1.6 (#20912)

cherry-pick1.6 simplify master+patch，remove ins when size != merge_size or has conflict slot  (#20941)

* simplify master+patch，remove ins when size != merge_size or has conflict slot
* test=develop

* add check nan / inf in downpour worker during training
* test=develop

* update pserver decay blocks

* update distributed notify handler

[cherry-pick] keep the size of symmetric padding is 2 for 2d and 3 for 3d. test=release/1.6 (#20903) (#20939)

* Fix Paddle Cloud role maker (#20860)

- fix jit::matmul bug 

input x, shape(m, k), weight, shape(k, n) 

* bug fix, test=develop

* Simplify third_party path in Python package
* Fix typo

* Serialize to pickle format (#20820)

test=develop

* save load problem fix and new feature add (#20823)

* fix persistable;

* fix save load bugs; test=develop

* fix bug; test=develop

* add example for new io api; test=develop

* addd example; test=develop

* test=document_fix

* test=release/1.6

test=release/1.6 test=document_fix

* add support for __get_item__ of Variable test=develop

* update the infer shape of matmul,  test=release/1.6

* add unittests of matmul, test=release/1.6

* change func names, test=release/1.6

* add dlpack include in third_party. test=develop

* test=develop, communicator_is_sgd_optimizer flags

【cherry-pick】 fix fill_constant shape with -1 and enhance cross_entropy test=release/1.6 (#20722) (#20728)

* fix fetch handler error with pslib

* fix distributed lookup table op with 1 pserver

* Fix communicator slow bug & fix communicator stop bug (#20366)

* test=develop,Fix communicator slow bug

* test=develop, delete if() in stop_worker()

* test=develop

* fix UT, test=develop

* fix bug in fetch handler, test=develop

* fix bug in fetch handler, test=develop

* test=develop, fix fetch barrier bug

* test=develop, bug fix

* test=develop, bug fix

* test=develop, fix bug

* test=develop,test=release/1.6

* move pool2d to add_quant_dequant_pass, test=develop

test=release/1.6, test=develop

* Support fp16 in fused_elemwise_activation_op.
* Fix unit testing in ONLY-CPU mode.

test=release/1.6

* bug fix: invalid learning rate decay in pserver async mode

* support dump multi file
test=develop

* dump fix num file
test=develop

test=release/1.6

* cherry-pick refine slim reader to support dataloader test=release/1.6

* cherry-pick add test for reader test=release/1.6

* cherry-pick rm checkpoint path test=release/1.6

* cherry-pick fix details test=release/1.6

* cherry-pick fix details test=release/1.6

* disable nccl test

* Update version.

* fix term core only

* fix transpiler error

* fix protobuf memory leak (#11177)

fix protobuf memory leak

* "change eigen mirror"

* test=document_fix

* test=document_fix