Merge pull request #25751 from simonkampe:fix-eigen-rowmajor

Add missing cv2eigen overload #25751

Fixes #16606

Add overloads to cv2eigen to handle eigen matrices of type
Eigen::Matrix<Tp_, Eigen::Dynamic, Eigen::Dynamic, Eigen::RowMajor>

### 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
- [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [ ] The feature is well documented and sample code can be built with the project CMake

modules/core/include/opencv2/core/eigen.hpp

@@ -287,6 +287,17 @@ void cv2eigen( const Mat& src,
     }
 }
 
+template<typename _Tp>  static inline
+void cv2eigen( const Mat& src,
+               Eigen::Matrix<_Tp, Eigen::Dynamic, Eigen::Dynamic, Eigen::RowMajor>& dst )
+{
+    CV_CheckEQ(src.dims, 2, "");
+    dst.resize(src.rows, src.cols);
+    const Mat _dst(src.rows, src.cols, traits::Type<_Tp>::value,
+             dst.data(), (size_t)(dst.outerStride()*sizeof(_Tp)));
+    src.convertTo(_dst, _dst.type());
+}
+
 // Matx case
 template<typename _Tp, int _rows, int _cols> static inline
 void cv2eigen( const Matx<_Tp, _rows, _cols>& src,
@@ -307,6 +318,17 @@ void cv2eigen( const Matx<_Tp, _rows, _cols>& src,
     }
 }
 
+template<typename _Tp, int _rows, int _cols> static inline
+void cv2eigen( const Matx<_Tp, _rows, _cols>& src,
+               Eigen::Matrix<_Tp, Eigen::Dynamic, Eigen::Dynamic, Eigen::RowMajor>& dst )
+{
+    CV_CheckEQ(src.dims, 2, "");
+    dst.resize(_rows, _cols);
+    const Mat _dst(_rows, _cols, traits::Type<_Tp>::value,
+                   dst.data(), (size_t)(dst.outerStride()*sizeof(_Tp)));
+    Mat(src).copyTo(_dst);
+}
+
 template<typename _Tp> static inline
 void cv2eigen( const Mat& src,
                Eigen::Matrix<_Tp, Eigen::Dynamic, 1>& dst )