Merge pull request #16717 from OrestChura:oc/goodFeatures

- cv::gapi::goodFeaturesToTrack() kernel is implemented
- tests (for exact check with cv::goodFeaturesToTrack() and for internal cases) are implemented
- a custom comparison function for vectors and a custom test fixture implemented
  - some posiible issues as wrong/inexact sorting of two compared vectors are
 not taken into account
- initializations of an input Mat using a picture from opencv_extra implemented (function from gapi_streaming_test used)

modules/gapi/src/api/kernels_imgproc.cpp

@@ -2,7 +2,7 @@
 // It is subject to the license terms in the LICENSE file found in the top-level directory
 // of this distribution and at http://opencv.org/license.html.
 //
-// Copyright (C) 2018 Intel Corporation
+// Copyright (C) 2018-2020 Intel Corporation
 
 
 #include "precomp.hpp"
@@ -97,6 +97,14 @@ GMat Canny(const GMat& src, double thr1, double thr2, int apertureSize, bool l2g
     return imgproc::GCanny::on(src, thr1, thr2, apertureSize, l2gradient);
 }
 
+cv::GArray<cv::Point2f> goodFeaturesToTrack(const GMat& image, int maxCorners, double qualityLevel,
+                                            double minDistance, const Mat& mask, int blockSize,
+                                            bool useHarrisDetector, double k)
+{
+    return imgproc::GGoodFeatures::on(image, maxCorners, qualityLevel, minDistance, mask, blockSize,
+                                      useHarrisDetector, k);
+}
+
 GMat RGB2Gray(const GMat& src)
 {
     return imgproc::GRGB2Gray::on(src);