LibJS: Implement correct object property ordering

This commit introduces a way to get an object's own properties in the
correct order. The "correct order" for JS object properties is first all
array-like index properties (numeric keys) sorted by insertion order,
followed by all string properties sorted by insertion order.

Objects also now print correctly in the repl! Before this commit:

courage ~/js-tests $ js
> ({ foo: 1, bar: 2, baz: 3 })
{ bar: 2, foo: 1, baz: 3 }

After:

courage ~/js-tests $ js
> ({ foo: 1, bar: 2, baz: 3 })
{ foo: 1, bar: 2, baz: 3 }

Libraries/LibJS/Runtime/ObjectConstructor.cpp

@@ -76,7 +76,7 @@ Value ObjectConstructor::get_own_property_names(Interpreter& interpreter)
             result->elements().append(js_string(interpreter, String::number(i)));
     }
 
-    for (auto& it : object->shape().property_table()) {
+    for (auto& it : object->shape().property_table_ordered()) {
         result->elements().append(js_string(interpreter, it.key));
     }
     return result;