message: flann: drop wrapping of Index class
  due to lifetime restrictions on passed 'features' parameter and its dangling pointers
  dangling pointer issue is fixed for OpenCV 4.5.1+
diff: @@ -131,26 +131,30 @@ struct CV_EXPORTS SearchParams : public IndexParams
  SearchParams( int checks = 32, float eps = 0, bool sorted = true );
  };
  -class CV_EXPORTS_W Index
  +class CV_EXPORTS Index
  {
  public:
  - CV_WRAP Index();
  - CV_WRAP Index(InputArray features, const IndexParams& params, cvflann::flann_distance_t distType=cvflann::FLANN_DIST_L2);
  + Index();
  +
  + /// @note 'features' must have extended lifetime (as cv::Mat) than this #Index instance (to avoid dangling pointers)
  + Index(InputArray features, const IndexParams& params, cvflann::flann_distance_t distType=cvflann::FLANN_DIST_L2);
  virtual ~Index();
  - CV_WRAP virtual void build(InputArray features, const IndexParams& params, cvflann::flann_distance_t distType=cvflann::FLANN_DIST_L2);
  - CV_WRAP virtual void knnSearch(InputArray query, OutputArray indices,
  + /// @note 'features' must have extended lifetime (as cv::Mat) than this #Index instance (to avoid dangling pointers)
  + virtual void build(InputArray features, const IndexParams& params, cvflann::flann_distance_t distType=cvflann::FLANN_DIST_L2);
  +
  + virtual void knnSearch(InputArray query, OutputArray indices,
  OutputArray dists, int knn, const SearchParams& params=SearchParams());
  - CV_WRAP virtual int radiusSearch(InputArray query, OutputArray indices,
  + virtual int radiusSearch(InputArray query, OutputArray indices,
  OutputArray dists, double radius, int maxResults,
  const SearchParams& params=SearchParams());
  - CV_WRAP virtual void save(const String& filename) const;
  - CV_WRAP virtual bool load(InputArray features, const String& filename);
  - CV_WRAP virtual void release();
  - CV_WRAP cvflann::flann_distance_t getDistance() const;
  - CV_WRAP cvflann::flann_algorithm_t getAlgorithm() const;
  + virtual void save(const String& filename) const;
  + virtual bool load(InputArray features, const String& filename);
  + virtual void release();
  + cvflann::flann_distance_t getDistance() const;
  + cvflann::flann_algorithm_t getAlgorithm() const;
  protected:
  cvflann::flann_distance_t distType;
  