fix CUDA build

CUDA implementation wants to convert std::vector<KeyPoint> <-> GpuMat.
There is no direct mapping from KeyPoint (mix of int/float fields)
into cv::Mat element type, so this conversion must be avoided.

Legacy mode is turned back for CUDA builds.

modules/core/CMakeLists.txt

@@ -63,5 +63,9 @@ ocv_target_link_libraries(${the_module} LINK_PRIVATE
     "${OPENCV_HAL_LINKER_LIBS}"
 )
 
+if(HAVE_CUDA)
+  ocv_target_compile_definitions(${the_module} PUBLIC OPENCV_TRAITS_ENABLE_DEPRECATED)
+endif()
+
 ocv_add_accuracy_tests()
 ocv_add_perf_tests()