Merge pull request #27547 from abhishek-gola:topk_layer_add

Added TopK layer with dynamic K support for new DNN engine #27547

This pull request adds TopK layer support to new DNN engine along with dynamic K support.

Initial version inherited from https://github.com/opencv/opencv/pull/26731. Credits to Abduragim.

Closes:
- https://github.com/opencv/opencv/issues/27061
- https://github.com/opencv/opencv/issues/25712

Also closes the topk issue for below issues but having (`Unsupported operations:        NonZero` for new dnn engine) which is unrelated to topk.
- https://github.com/opencv/opencv/issues/23663 
- https://github.com/opencv/opencv/issues/23297

### Pull Request Readiness Checklist

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/init.cpp

@@ -222,6 +222,7 @@ void initializeLayerFactory()
     CV_DNN_REGISTER_LAYER_CLASS(ScatterND,      ScatterNDLayer);
     CV_DNN_REGISTER_LAYER_CLASS(Tile,           TileLayer);
     CV_DNN_REGISTER_LAYER_CLASS(TopK,           TopKLayer);
+    CV_DNN_REGISTER_LAYER_CLASS(TopK2,          TopK2Layer);
 
     CV_DNN_REGISTER_LAYER_CLASS(Quantize,         QuantizeLayer);
     CV_DNN_REGISTER_LAYER_CLASS(Dequantize,       DequantizeLayer);