Platform: Implement WheelUp/Down analog to Sdl2Application

... for better portability.

Signed-off-by: Squareys <squareys@googlemail.com>

src/Magnum/Platform/GlfwApplication.cpp

@@ -178,6 +178,12 @@ void GlfwApplication::staticMouseEvent(GLFWwindow*, int button, int action, int)
 void GlfwApplication::staticMouseScrollEvent(GLFWwindow*, double xoffset, double yoffset) {
     MouseScrollEvent e(Vector2d{xoffset, yoffset});
     _instance->mouseScrollEvent(e);
+
+    if(yoffset != 0.0) {
+        MouseEvent e1((yoffset > 0.0) ? MouseEvent::Button::WheelUp : MouseEvent::Button::WheelDown);
+        _instance->mousePressEvent(e);
+        _instance->mousePressEvent(e1);
+    }
 }
 
 void GlfwApplication::staticErrorCallback(int, const char* description) {

src/Magnum/Platform/GlfwApplication.h

@@ -665,6 +665,9 @@ class GlfwApplication::MouseEvent: public GlfwApplication::InputEvent {
             Button6 = GLFW_MOUSE_BUTTON_6,        /**< Mouse button 6 */
             Button7 = GLFW_MOUSE_BUTTON_7,        /**< Mouse button 7 */
             Button8 = GLFW_MOUSE_BUTTON_8,        /**< Mouse button 8 */
+
+            WheelUp = GLFW_MOUSE_BUTTON_LAST + 1,   /**< Mouse wheel up */
+            WheelDown = GLFW_MOUSE_BUTTON_LAST + 2, /**< Mouse wheel down */
         };
 
         /** @brief Button */