Merge pull request #16616 from alalek:dnn_fix_input_shape

* dnn: fix processing of input shapes

- importer: avoid using of .setInput() => .setInputShape()
- setInput: shape limitation check (partial)

* dnn(test): test .setInput() in readNet()

modules/dnn/include/opencv2/dnn/dnn.hpp

@@ -484,6 +484,10 @@ CV__DNN_EXPERIMENTAL_NS_BEGIN
          */
         CV_WRAP void setInputsNames(const std::vector<String> &inputBlobNames);
 
+        /** @brief Specify shape of network input.
+         */
+        CV_WRAP void setInputShape(const String &inputName, const MatShape& shape);
+
         /** @brief Runs forward pass to compute output of layer with name @p outputName.
          *  @param outputName name for layer which output is needed to get
          *  @return blob for first output of specified layer.

modules/dnn/include/opencv2/dnn/shape_utils.hpp

@@ -138,6 +138,16 @@ static inline MatShape shape(const UMat& mat)
     return shape(mat.size.p, mat.dims);
 }
 
+#if 0  // issues with MatExpr wrapped into InputArray
+static inline
+MatShape shape(InputArray input)
+{
+    int sz[CV_MAX_DIM];
+    int ndims = input.sizend(sz);
+    return shape(sz, ndims);
+}
+#endif
+
 namespace {inline bool is_neg(int i) { return i < 0; }}
 
 static inline MatShape shape(int a0, int a1=-1, int a2=-1, int a3=-1)