Add Similarity Net as unit test. During the unit test, we found three problems:

1. The run_program_op has memory optimization error when running dy2stat net multiple times.
2. The support for SelectedRows can cause problem in dy2stat.
3. The return grammar has problem.

This PR fixes the 1. problem but modify codes for the 2. 3. problems to make PR smaller. I will fix those two problems in the next PR(s)

* Add the imperative quantization aware training.
*  This is the python part of Imperative QAT. test=develop

* fix softmax_with_cross_entropy cuda kernel overflow bug, test=develop

* replace old macro & for condition, test=develop

* polish details, test=develop

* add explicit specialization

* add skiplayernorm vector load if available

* test=develop

* polish pe exception process logic, test=develop

* fix unittest, test=develop

* add unittests, test=develop

Use vector instruction (LDG.128) to improve qkv transpose. It
provides 1.4X speedup at same GPU base frequency.
test=develop

remove useless property

test=develop

* fix concat shape error
test=develop

* add retry for prefetch

* Revert "Fix/sync barrier (#25016)"

This reverts commit be6a315f.

* reopen dist UT, test=develop

* remove fl UT, test=develop

* fix bn & in in dy, test=develop

* update instance_norm,test=develop

* fix bugs,test=develop

* add more case in unittest,test=develop

* fix,test=develop

* fix,test=develop

* add device_worker for pipeline, test=develop

* cat bad alloc exception; test=develop

* add unitest; test=develop

* move bad alloc catch to the first place; test=develop

* polish error message; test=develop

* polish error message; test=develop

* add mutex header; test=develop

* fix multhead matmul's instable
test=develop

* fix multihead matmul bug
test=develop

* fix converage problem
test=develop

* refine PADDLE_ENFORCE
test=develop

* add paddle.fleet.DistributedStrategy for 2.0

* modify pipeline optimizer, test=develop

* add mish op. test=develop

* fix PADDLE_ENFORCE and refine the description
test=develop

* Add `matrix_nms_op`

test=develop

* Make ci happy

test=develop

* Exit early when no detection

test=develop

* Fix license year

test=develop

* Output index as well

test=develop

* Match nms2 lod behavior and add `return_index` flag

test=develop

* Make CI happy

test=develop

* Fix wording

test=develop

* refactor dynamic dso search func, test=develop

* polish details, test=develop

* polish detail based review comments, test=develop

* revert string type change, test=develop

* add encrypt api for inference lib

* test=develop, fix_embedding

* Modify tmp var name prefix in dygraph test=develop

* refine comment test=develop