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

diff --cc cmake/OpenCVUtils.cmake
Simple merge

diff --cc doc/tutorials/core/mat_the_basic_image_container/mat_the_basic_image_container.markdown
Simple merge

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

diff --cc modules/dnn/src/onnx/onnx_importer.cpp
Simple merge

diff --cc modules/dnn/src/tensorflow/tf_importer.cpp
index 10670bf,01fa0df..4bd09ad
--- 1/modules/dnn/src/tensorflow/tf_importer.cpp
--- 2/modules/dnn/src/tensorflow/tf_importer.cpp
+++ b/modules/dnn/src/tensorflow/tf_importer.cpp
@@@ -516,8 -551,8 +557,9 @@@ protected
  
  private:
      void addPermuteLayer(const int* order, const std::string& permName, Pin& inpId);
+     void setPadding(LayerParams &layerParams, const tensorflow::NodeDef &layer, std::string& inputName, float value = 0.);
  
 +    friend class LayerHandler;
      typedef void (TFImporter::*TFImporterNodeParser)(tensorflow::GraphDef&, const tensorflow::NodeDef&, LayerParams&);
      typedef std::map<std::string, TFImporterNodeParser> DispatchMap;
  
@@@ -558,20 -593,31 +600,45 @@@
      void parseCustomLayer        (tensorflow::GraphDef& net, const tensorflow::NodeDef& layer, LayerParams& layerParams);
  };
  
+ void TFImporter::setPadding(LayerParams &layerParams, const tensorflow::NodeDef &layer, std::string& inputName, float value)
+ {
+     setPadMode(layerParams, layer);
+     int64_t pads[8];
+ 
+     if (!getExplicitPadding(layerParams, layer, pads))
+     {
+         return;
+     }
+ 
+     LayerParams padLp;
+     padLp.name = layer.name() + "/pad";
+     padLp.type = "Padding";
+     padLp.set("paddings", DictValue::arrayInt(pads, sizeof(pads) / sizeof(pads[0])));
+     padLp.set("value", value);
+ 
+     int id = dstNet.addLayer(padLp.name, padLp.type, padLp);
+     layer_id[padLp.name] = id;
+ 
+     connect(layer_id, dstNet, parsePin(inputName), id, 0);
+     inputName = padLp.name;
+ 
+     layerParams.set("pad_mode", "VALID");
+ }
+ 
 +class LayerHandler
 +{
 +public:
 +    LayerHandler(TFImporter* importer_);
 +    ~LayerHandler() = default;
 +
 +    bool handleMissing(const opencv_tensorflow::NodeDef& layer);
 +    void handleFailed(const opencv_tensorflow::NodeDef& layer);
 +
 +private:
 +    TFImporter* importer;
 +    std::set<std::string> layers;
 +};
 +
  const TFImporter::DispatchMap TFImporter::buildDispatchMap()
  {
      static DispatchMap dispatch;

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

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

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