Merge pull request #25146 from mshabunin:cpp-contours

Reworked findContours to reduce C-API usage #25146

What is done:
* rewritten `findContours` and `icvApproximateChainTC89` using C++ data structures
* extracted LINK_RUNS mode to separate new public functions - `findContoursLinkRuns` (it uses completely different algorithm)
* ~added new public `cv::approximateChainTC89`~ - **❌ decided to hide it**
* enabled chain code output (method = 0, no public enum value for this in C++ yet)
* kept old function as `findContours_old` (exported, but not exposed to user)
* added more tests for findContours (`test_contours_new.cpp`), some tests compare results of old function with new one. Following tests have been added:
  * contours of random rectangle
  * contours of many small (1-2px) blobs
  * contours of random noise
  * backport of old accuracy test
  * separate test for LINK RUNS variant

What is left to be done (can be done now or later):
* improve tests: 
  * some tests have limited verification (e.g. only verify contour sizes)
  * perhaps reference data can be collected and stored
  * maybe more test variants can be added (?)
* add enum value for chain code output and a method of returning starting points (e.g. first 8 elements of returned `vector<uchar>` can represent 2 int point coordinates)
* add documentation for new functions - **✔️ DONE**
* check and improve performance (my experiment showed 0.7x-1.1x some time ago)
* remove old functions completely (?)
* change contour return order (BFS) or allow to select it (?)
* return result tree as-is (?) (new data structures should be exposed, bindings should adapt)

modules/imgproc/test/test_contours.cpp

@@ -39,6 +39,7 @@
 //
 //M*/
 
+#include "opencv2/imgproc/types_c.h"
 #include "test_precomp.hpp"
 #include <opencv2/highgui.hpp>
 
@@ -459,7 +460,6 @@ TEST(Imgproc_FindContours, hilbert)
     dilate(img, img, Mat());
     vector<vector<Point> > contours;
     findContours(img, contours, noArray(), RETR_LIST, CHAIN_APPROX_SIMPLE);
-    printf("ncontours = %d, contour[0].npoints=%d\n", (int)contours.size(), (int)contours[0].size());
     img.setTo(Scalar::all(0));
 
     drawContours(img, contours, 0, Scalar::all(255), 1);
@@ -530,10 +530,12 @@ TEST(Imgproc_FindContours, regression_4363_shared_nbd)
 
     if (found)
     {
+        ASSERT_EQ(contours.size(), hierarchy.size());
         EXPECT_LT(hierarchy[index][3], 0) << "Desired result: (7,9) has no parent - Actual result: parent of (7,9) is another contour. index = " << index;
     }
 }
 
+
 TEST(Imgproc_PointPolygonTest, regression_10222)
 {
     vector<Point> contour;