Merge remote-tracking branch 'upstream/3.4' into merge-3.4

diff --cc modules/core/include/opencv2/core/cuda/functional.hpp
Simple merge

diff --cc modules/core/include/opencv2/core/cvdef.h
Simple merge

diff --cc modules/core/src/merge.cpp
Simple merge

diff --cc modules/core/test/test_mat.cpp
Simple merge

diff --cc modules/dnn/src/layers/convolution_layer.cpp
Simple merge

diff --cc modules/imgproc/include/opencv2/imgproc.hpp
Simple merge