Onnx conformance tests

* Add ONNX conformance tests

* dnn(test): add filters for ONNX conformance tests

* add filter lists for OCV backend

* address review comments

* move test_clip_inbounds to all_denylist

* address clip issue

* avoid empty lists
Co-authored-by: NAlexander Alekhin <alexander.a.alekhin@gmail.com>

- CMake option: OPENCV_DNN_IE_NN_BUILDER_2019

* Support nGraph

* Fix resize

- don't share .cpp files (PCH support is broken)

* Fix precision in tests for MyriadX

* Fix ONNX tests

* Add output range in ONNX tests

* Skip tests on Myriad OpenVINO 2018R5

* Add detect MyriadX

* Add detect MyriadX on OpenVINO R5

* Skip tests on Myriad next version of OpenVINO

* dnn(ie): VPU type from environment variable

* dnn(test): validate VPU type

* dnn(test): update DLIE test skip conditions

DNN backends registry (#13332)

* Added dnn backends registry

* dnn: process DLIE/FPGA target

- OpenCL tests didn't run any OpenCL kernels
- use real configuration from existed models (the first 100 cases)
- batch size = 1

* Update Intel's Inference Engine deep learning backend

* Remove cpu_extension dependency

* Update Darknet accuracy tests

add a corresponding test

https://github.com/opencv/opencv_contrib/tree/e6f63c7a38ca40c5dc33e38736e3027e3528d6cb/modules/dnn

plus minor edits and fixes