LibWeb: Add internals.wheel() to simulate mouse wheel events

This function allows us to write tests for scrolling scenarios where
the events are processed by the EventHandler.

Userland/Libraries/LibWeb/Internals/Internals.h

@@ -26,6 +26,7 @@ public:
     void commit_text();
 
     void click(double x, double y);
+    void wheel(double x, double y, double delta_x, double delta_y);
 
     WebIDL::ExceptionOr<bool> dispatch_user_activated_event(DOM::EventTarget&, DOM::Event& event);