Merge pull request #29293 from MaitreyeeDeshmukh:fix/opengl-sample-ptcloud-missing-include

fix: include ptcloud header and dependency for opengl_testdata_generator sample #29293

## Summary
Fixes the build failure in samples/opengl/opengl_testdata_generator.cpp on the 5.x 
branch when building with BUILD_EXAMPLES=ON.

## Root cause
The sample uses `loadMesh`, `TriangleShadingType`, and `TriangleCullingMode`, all 
declared in `modules/ptcloud/include/opencv2/ptcloud.hpp`. The sample did not 
include this header, and `samples/opengl/CMakeLists.txt` did not list 
`opencv_ptcloud` as a required dependency, so the ptcloud module headers/libs 
were not available when compiling this sample.

## Changes
- Added `#include "opencv2/ptcloud.hpp"` to opengl_testdata_generator.cpp
- Added `opencv_ptcloud` to `OPENCV_OPENGL_SAMPLES_REQUIRED_DEPS` in 
  samples/opengl/CMakeLists.txt

## Acceptance criteria
- [x] opengl_testdata_generator.cpp compiles with BUILD_EXAMPLES=ON
- [x] ptcloud module dependency declared so build system links it correctly

Closes #29292

samples/opengl/CMakeLists.txt

@@ -14,6 +14,7 @@ SET(OPENCV_OPENGL_SAMPLES_REQUIRED_DEPS
   opencv_imgproc
   opencv_imgcodecs
   opencv_geometry
+  opencv_ptcloud
   opencv_videoio
   opencv_highgui)
 ocv_check_dependencies(${OPENCV_OPENGL_SAMPLES_REQUIRED_DEPS})

samples/opengl/opengl_testdata_generator.cpp

@@ -20,6 +20,7 @@
 #include "opencv2/imgproc.hpp"
 #include "opencv2/highgui.hpp"
 #include "opencv2/geometry.hpp"
+#include "opencv2/ptcloud.hpp"
 
 using namespace std;
 using namespace cv;
@@ -510,17 +511,17 @@ int main(int argc, char* argv[])
 
         for (const auto& res : resolutions)
         {
-            for (const auto shadingPair : shadingTxt)
+            for (const auto& shadingPair : shadingTxt)
             {
                 cv::TriangleShadingType shadingType = shadingPair.first;
                 std::string shadingName = shadingPair.second;
 
-                for (const auto cullingPair : cullingTxt)
+                for (const auto& cullingPair : cullingTxt)
                 {
                     cv::TriangleCullingMode cullingMode = cullingPair.first;
                     std::string cullingName = cullingPair.second;
 
-                    for (const auto modelPair : modelTxt)
+                    for (const auto& modelPair : modelTxt)
                     {
                         ModelType modelType = modelPair.first;
                         std::string modelName = modelPair.second;