Add ocl version BackgroundSubtractorKNN (#10553)
* Add ocl version bgfg_knn
* Add ocl KNN perf test
* ocl KNN: Avoid unnecessary initializing when non-UMat parameters are used
* video: turn off OpenCL for color KNN on Intel devices
due performance degradation
* video: turn off KNN OpenCL on Apple devices with Intel iGPU
due process freeze during clBuildProgram() call