Merge pull request #24196 from dkurt:ov_backend_cleanups

Use ngraph::Output in OpenVINO backend wrapper #24196

### Pull Request Readiness Checklist

resolves https://github.com/opencv/opencv/issues/24102

* Use `ngraph::Output<ngraph::Node>>` insead of `std::shared_ptr<ngraph::Node>` as a backend wrapper. It lets access to multi-output nodes: https://github.com/opencv/opencv/blob/588ddf1b181aa7243144b27d65fc7690fb89e344/modules/dnn/src/net_openvino.cpp#L501-L504
* All layers can be customizable with OpenVINO >= 2022.1. nGraph reference code used for default layer implementation does not required CPU plugin also (might be tested by commenting CPU plugin at `/opt/intel/openvino/runtime/lib/intel64/plugins.xml`).
* Correct inference if only intermediate blobs requested.


See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [x] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [x] The feature is well documented and sample code can be built with the project CMake

modules/dnn/src/layers/region_layer.cpp

@@ -466,7 +466,7 @@ public:
                                         const std::vector<Ptr<BackendNode> >& nodes) CV_OVERRIDE
     {
         auto& input = nodes[0].dynamicCast<InfEngineNgraphNode>()->node;
-        auto parent_shape = input->get_shape();
+        auto parent_shape = input.get_shape();
         int64_t b = parent_shape[0];
         int64_t h = parent_shape[1];
         int64_t w = parent_shape[2];
@@ -567,7 +567,7 @@ public:
             int hNorm, wNorm;
             if (nodes.size() > 1)
             {
-                auto node_1_shape = nodes[1].dynamicCast<InfEngineNgraphNode>()->node->get_shape();
+                auto node_1_shape = nodes[1].dynamicCast<InfEngineNgraphNode>()->node.get_shape();
                 hNorm = node_1_shape[2];
                 wNorm = node_1_shape[3];
             }