Further optimization of Conv2D, fused Conv_Add_Activation, bring latest code from ficus OpConv.fx. (#22401)

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

@@ -256,6 +256,9 @@ CV__DNN_INLINE_NS_BEGIN
     {
     public:
         static Ptr<BaseConvolutionLayer> create(const LayerParams& params);
+        bool fusedActivation = false;
+        bool fusedAdd = false;
+        bool isConv2D = false; // Should be deleted after fastconv branch support Conv1D and Conv3D.
     };
 
     class CV_EXPORTS ConvolutionLayerInt8 : public BaseConvolutionLayer