LibJS: Initial class implementation; allow super expressions in object

literal methods; add EnvrionmentRecord fields and methods to
LexicalEnvironment

Adding EnvrionmentRecord's fields and methods lets us throw an exception
when |this| is not initialized, which occurs when the super constructor
in a derived class has not yet been called, or when |this| has already
been initialized (the super constructor was already called).

Libraries/LibJS/Runtime/Object.cpp

@@ -437,7 +437,7 @@ bool Object::define_accessor(PropertyName property_name, Function& getter_or_set
             accessor = &existing_property.as_accessor();
     }
     if (!accessor) {
-        accessor = Accessor::create(interpreter(), nullptr, nullptr);
+        accessor = Accessor::create(interpreter(), global_object(), nullptr, nullptr);
         bool definition_success = define_property(property_name, accessor, attributes, throw_exceptions);
         if (interpreter().exception())
             return {};