Merge pull request #14697 from l-bat:Slice_ONNX

* Support Slice layer in ONNX importer

* Add IE support

* Fix ONNX importer

* Fix Slice

modules/dnn/test/test_onnx_importer.cpp

@@ -245,6 +245,11 @@ TEST_P(Test_ONNX_layers, Reshape)
     testONNXModels("unsqueeze");
 }
 
+TEST_P(Test_ONNX_layers, Slice)
+{
+    testONNXModels("slice");
+}
+
 TEST_P(Test_ONNX_layers, Softmax)
 {
     testONNXModels("softmax");