GAPI: Add normalize kernel in G-API (#13721)

* Add normalize kernel in G-API

In addition add several tests on new kernel

* Fix indentations and normalize test structure

* Move normalize kernel from imgproc to core

Set default parameter ddepth to -1

* Fix alignment

instead of get_local_size(0) and dynamic local memory allocation

* Optical Flow rework to use wide universal intrinsics

* remove if (useSIMD) check as review requested

YUV42x color conversions rewritten to wide intrinsics (#13708)

* a*b+c -> fma

* YUV420sp2RGB initially vectorized

* shorter var names

* loops by 4

* yuv420p2rgb vectorized

* yuv422toRGB vectorized

* reg arrays

* rgb2yuv420 vectorized

* warnings fixed

* try to fix align error

SVM sigmoid kernel fix (issue #13621) (#13718)

* Added test for sigmoid case for retrieving support vectors

* undo unhelpful test

* add test for sigmoid SVM with data that is easily separable into two concentric circles

* Update sigmoid kernel to use tanh(gamma * <x, y> + coef0) instead of -tanh(gamma * <x, y> + coef0)

* remove unnecessary constraint on coef0

* cleanup

* fixing inappropriate use of doubles

* Add f to float literal

* replace CV_Assert with ASSERT_EQ where appropriate

* spatialGradient() reworked to use wide universal intrinsics

* Moved row pointers inside loops

add messages to avoid silent kernel destruction

* Added DMatch bindings

* Added CR which was accidently removed to maintain consistency

* Removed trailing white-space

* imgproc: cleanup medianBlur_8u_O1 code

Unnecessary per-channel buffers: H[c] / lut[c]

* imgproc(medianBlur_8u_O1): use CV_SIMD_WIDTH for alignment

PyrDown: Fix bug #12961 (#13672)

* Force unaligned pointer and create test

* More cross-platform solution

* MSVC expects a proper order

* Remove useless clang macro

* Return vector of MetaArg instead of MatDesc and fix test with ADL check

* Fix construction of vector

* Change names and tests according to review
Also add GAPI_EXPORTS prefix for two ostream operators

* Add note about building for pkg-config

* minor fixes