Merge pull request #25354 from LaurentBerger:uiname

Add cv::currentUIFramework #25354

issue https://github.com/opencv/opencv/issues/25329

### 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
- [ ] 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.
- [x] The feature is well documented and sample code can be built with the project CMake

modules/highgui/include/opencv2/highgui.hpp

@@ -285,6 +285,15 @@ The function destroyAllWindows destroys all of the opened HighGUI windows.
  */
 CV_EXPORTS_W void destroyAllWindows();
 
+
+/** @brief HighGUI backend used.
+
+The function returns HighGUI backend name used: could be COCOA, GTK2/3, QT, WAYLAND or WIN32.
+Returns empty string if there is no available UI backend.
+ */
+CV_EXPORTS_W const std::string currentUIFramework();
+
+
 CV_EXPORTS_W int startWindowThread();
 
 /** @brief Similar to #waitKey, but returns full key code.