Merge pull request #13851 from TolyaTalamanov:at/new-kernel-package-design

G-API: Kernel package design (#13851)

* Remove cv::unite_policy from API

* Add check that all id in kernel package are unique

* Refactor checker id procedure

* Remove cv::gapi::GLookupOrder from API

* Implement cv::gapi::use_only

* Fix samples

* Fix docs

* Fix comments to review

* Remove unite_policy

* Fix GKernelPackage::backends()

* Fix comments to review

* Fix all_unique

* Fix comments to review

* Fix comments to review

* Remove out of date tests

samples/cpp/tutorial_code/gapi/porting_anisotropic_image_segmentation/porting_anisotropic_image_segmentation_gapi_fluid.cpp

@@ -65,8 +65,7 @@ int main()
     // Prepare the kernel package and run the graph
     cv::gapi::GKernelPackage fluid_kernels = cv::gapi::combine        // Define a custom kernel package:
         (cv::gapi::core::fluid::kernels(),                            // ...with Fluid Core kernels
-         cv::gapi::imgproc::fluid::kernels(),                         // ...and Fluid ImgProc kernels
-         cv::unite_policy::KEEP);
+         cv::gapi::imgproc::fluid::kernels());                        // ...and Fluid ImgProc kernels
     //! [kernel_pkg]
     //! [kernel_hotfix]
     fluid_kernels.remove<cv::gapi::imgproc::GBoxFilter>();            // Remove Fluid Box filter as unsuitable,