Merge pull request #25822 from mqcmd196:gtk3-gl-support

Support OpenGL GTK3 New API #25822

Fixes #20001

GSoC2024 Project

### 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

cmake/OpenCVFindLibsGUI.cmake

@@ -63,7 +63,7 @@ endif()
 ocv_update(OpenGL_GL_PREFERENCE LEGACY)
 ocv_clear_vars(HAVE_OPENGL HAVE_QT_OPENGL)
 if(WITH_OPENGL)
-  if(WITH_WIN32UI OR (HAVE_QT AND QT_QTOPENGL_FOUND) OR HAVE_GTKGLEXT)
+  if(WITH_WIN32UI OR (HAVE_QT AND QT_QTOPENGL_FOUND) OR HAVE_GTK3 OR (HAVE_GTK AND NOT HAVE_GTK3 AND HAVE_GTKGLEXT))
     find_package (OpenGL QUIET)
     if(OPENGL_FOUND)
       set(HAVE_OPENGL TRUE)