Merge pull request #28179 from Kumataro:fix28178

js: add C++17 requirement check for Emscripten 4.0.20+ #28179
 
Close https://github.com/opencv/opencv/issues/28178

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

doc/js_tutorials/js_setup/js_setup/js_setup.markdown

@@ -84,7 +84,12 @@ Building OpenCV.js from Source
     @endcode
 
     @note
-    It requires `python` and `cmake` installed in your development environment.
+    - It requires `python` and `cmake` installed in your development environment.
+    - To build with Emscripten 4.0.20 or later, append --cmake_option="-DCMAKE_CXX_STANDARD=17" .
+      Embind requires C++17 or later since Emscripten 4.0.20.
+      @code{.bash}
+      emcmake python ./opencv/platforms/js/build_js.py build_js --cmake_option="-DCMAKE_CXX_STANDARD=17"
+      @endcode
 
 -#  [Optional] To build the OpenCV.js loader, append `--build_loader`.