Implement camera viewfinder for Android via OpenGL

Documentation says:

>The Qt Multimedia Widgets module is not supported on Android, which means video display is only available using the VideoOutput and the Video QML Type.

But widget-based camera is much more powerful and useful than QML based. And this is not only one possible way to implement camera viewfinder. It is possible get needed result using QAbstractVideoSurface and QOpenGLWidget. Here (Russian) is the brief description of this method. It allows camera example work on Android devices without QML. I urge implement this method inside QCameraViewfinder class only for Android using conditional compilation.