LibJS+LibWeb: Move native JS functions into dedicated member functions

Instead of implementing every native function as a lambda function,
use static member functions instead.

This makes it easier to navigate the code + backtraces look nicer. :^)

Libraries/LibWeb/Bindings/EventTargetWrapper.h

@@ -42,6 +42,8 @@ public:
 private:
     virtual const char* class_name() const override { return "EventTargetWrapper"; }
 
+    static JS::Value add_event_listener(JS::Interpreter&);
+
     NonnullRefPtr<EventTarget> m_impl;
 };