[G-API]: Performance tests for KalmanFilter
* Kalman perf.tests and some tests refactoring
* Input generation moved to a separate function; Slowest case sneario testing added
* Generating refactored
* Generating refactoring
* Addressing comments
- kernel added to a cv::gapi::video namespace
- tests to check a kernels (based on cv::video tests for cv::buildOpticalFlowPyramid())
- tests for a combined G-API-pipeline (buildOpticalFlowPyramid() -> calcOpticalFlowPyrLK())
- tests for internal purposes added
- custom function for comparison in tests implemented
- opencv_gapi module is linked with opencv_video module (optional dependency)
- kernels added to a new cv::gapi::video namespace and a brand new files created to provide gapi_video environment
- there are 2 different kernels as G-API should provide GMat AND GArray<GMat> implementation: cv::calcOptFlowPyrLK doesn't calculate pyramids if vector<Mat> is given so just the cast GMat -> GArray<GMat> wouldn't represent all the cv:: functionality
- tests to check both kernels (based on cv::video tests for cv::calcOpticalFlowPyrLK())
- tests for internal purposes added
- vectors<T> comparison in tests implemented
- new (and old too) common test structures refactored to avoid code copypasting
- "modules/gapi/test/common/gapi_video_tests_common.hpp" created to share some code snippets between perf and acc tests and avoid code copypasting
