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

diff --cc modules/dnn/src/tensorflow/tf_graph_simplifier.cpp
Simple merge

diff --cc modules/dnn/test/test_tf_importer.cpp
Simple merge

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

diff --cc modules/imgproc/test/test_filter.cpp
Simple merge