* NV12 Ref impl: Align with Legacy NV12 conversion
Little-endian tricks are completely not needed finally
Basic tests of OV20 preprocessing vs Legacy preprocessing:
- Mean/Scale
- Resize (Linear vs Bilinear)
- NV12 color conversion
* Register Template plugin in legacy core before CNNNetwork compliance test
NV12: round to nearest integer for 'u8' mode
Fix preprocess-reference NV12 tests (swap U & V)
* Decreased default threshold and use random distribution for inputs generation
* Added tests RefImpl vs OpenCV - NV12 color conversion
Added CPU accuracy tests + nightly (including all RGB color combinations)
* Fix build issue after rebase
* Remove test code
* Fix comments
Disable OpenCV tests on CI (some machines can't load opencv_imgproc during test)