More fixes for G-API tests (#13251)

* scalar comparator and more fixes for tests

* add weighted aligned

* white space

* more white space

* Add weighted test accuracy check enabled

GAPI (fluid): optimization of Separable filter (#13221)

* GAPI (fluid): Separable filter: performance test

* GAPI (fluid): enable all performance tests

* GAPI: separable filters: alternative code for Sobel

* GAPI (fluid): hide unused old code for Sobel filter

* GAPI (fluid): especial code for Sobel if U8 into S16

* GAPI (fluid): back to old code for Sobel

* GAPI (fluid): run_sepfilter3x3_impl() with CPU dispatcher

* GAPI (fluid): run_sepfilter3x3_impl(): fix compiler warnings

* GAPI (fluid): new engine for separable filters (but Sobel)

* GAPI (fluid): new performance engine for Sobel

* GAPI (fluid): Sepfilters performance: fixed compilation error

Add URLs, harmonise formatting, and fix parse error in bibliography (#13228)

* Fixed parse error in bibliography

* Removed extra curly braces

* harmonized whitespace

* changed organisation -> publisher where appropriate. Organisation is intended as the author's organisation, not the publishing.

* harmonized capitalisation and whitespace

* Add links to about 1/3 of references

Use a global dedicated mutex to make sure initialize once and
protect command buffer pool and queue.
Signed-off-by: Wu Zhiwen <zhiwen.wu@intel.com>

created from RAW memory buffers (without proper lifetime management)

- don't require "OPENCV_PYTHON{2,3}_INSTALL_PATH" if OPENCV_SKIP_PYTHON_LOADER=ON
- avoid unnecessary relative paths in generated config-X.Y.py

* cmake: install 'legacy/constants_c.h' files

* samples: add compatibility test code

Reduce input size for OpenPose tests

* custom OpenCL G-API kernel draft

* clean up and warnings fix

* more warnings

* white space

* new blank line at the EOF removed

* HAVE_OPENCL guard

* remove unnecessary ocl API call

* remove sum test workaround

* check if opencl activated

* fix std::str warning

* CPU fall back for symm7x7

* gpu test kernel draft

* adjust have opencl guard

* more guards

* one more attempt to adjust guards

* empty stub files and kernel source files creation in the test directory

* try to force auto generation

* one more attempt to force build

* remove symm7x7 custom from gapi module

* looks like that this version works properly on Win desktop

* clean up

* more clean up

* address some suggestions from Dmitry's review

* const kernel coefficients

* CV_Error in kernel + try to fix cpu fallback

* CV_Error_ instead CV_Error

* everything in one gapi_gpu_test.cpp

* fix warning

* remove kernel generation, add kernel string

* avoid generated code and ocl internal namespace

* fix misprint

* c_str

CMake option: WITH_ADE=OFF

* dnn/Vulkan: don't init Vulkan runtime if using other backend/target

Don't need to explictly call a init API but will automatically
init Vulkan environment the first time to use an VkCom object.
Signed-off-by: Wu Zhiwen <zhiwen.wu@intel.com>

* dnn/Vulkan: depress compilier warning for "-Wsign-promo"
Signed-off-by: Wu Zhiwen <zhiwen.wu@intel.com>