LibJS+LibWeb: Pass prototype to Object constructor

Everyone who constructs an Object must now pass a prototype object when
applicable. There's still a fair amount of code that passes something
fetched from the Interpreter, but this brings us closer to being able
to detach prototypes from Interpreter eventually.

Libraries/LibJS/Runtime/Object.h

@@ -38,7 +38,9 @@ namespace JS {
 
 class Object : public Cell {
 public:
-    Object();
+    static Object* create_empty(Interpreter&, GlobalObject&);
+
+    explicit Object(Object* prototype);
     virtual ~Object();
 
     Shape& shape() { return *m_shape; }