Merge pull request #26590 from Kumataro:fix26589

Support C++20 standard #26590

Close https://github.com/opencv/opencv/issues/26589
Related https://github.com/opencv/opencv_contrib/pull/3842
Related: https://github.com/opencv/opencv/issues/20269

- do not arithmetic enums and ( different enums or floating numeric) 
- remove unused variable

### 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
- [x] 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/src/window.cpp

@@ -219,7 +219,7 @@ CV_IMPL void cvSetWindowProperty(const char* name, int prop_id, double prop_valu
     //change between fullscreen or not.
     case cv::WND_PROP_FULLSCREEN:
 
-        if (prop_value != cv::WINDOW_NORMAL && prop_value != cv::WINDOW_FULLSCREEN)  // bad argument
+        if ((int)prop_value != cv::WINDOW_NORMAL && (int)prop_value != cv::WINDOW_FULLSCREEN)  // bad argument
             break;
 
         #if defined (HAVE_QT)

modules/highgui/src/window_gtk.cpp

@@ -2177,7 +2177,7 @@ public:
         switch (prop)
         {
         case cv::WND_PROP_FULLSCREEN:
-            if (value != cv::WINDOW_NORMAL && value != cv::WINDOW_FULLSCREEN)  // bad arg
+            if ((int)value != cv::WINDOW_NORMAL && (int)value != cv::WINDOW_FULLSCREEN)  // bad arg
                 break;
             setModeWindow_(window, value);
             return true;

modules/highgui/src/window_w32.cpp

@@ -2805,7 +2805,7 @@ public:
         switch ((WindowPropertyFlags)prop)
         {
         case WND_PROP_FULLSCREEN:
-            if (value != WINDOW_NORMAL && value != WINDOW_FULLSCREEN)  // bad arg
+            if ((int)value != WINDOW_NORMAL && (int)value != WINDOW_FULLSCREEN)  // bad arg
                 break;
             setModeWindow_(window, (int)value);
             return true;