Merge pull request #20442 from JulieBar:gru_layer

* Add initialization and inference for GRU layer

* fix issues found on review

modules/dnn/src/init.cpp

@@ -139,6 +139,7 @@ void initializeLayerFactory()
     CV_DNN_REGISTER_LAYER_CLASS(FlowWarp,       FlowWarpLayer);
 
     CV_DNN_REGISTER_LAYER_CLASS(LSTM,           LSTMLayer);
+    CV_DNN_REGISTER_LAYER_CLASS(GRU,            GRULayer);
 }
 
 CV__DNN_INLINE_NS_END