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/Tests/Object.getOwnPropertyNames.js

@@ -1,13 +1,19 @@
 load("test-common.js");
 
 try {
-    var names = Object.getOwnPropertyNames([1, 2, 3]);
+    let names = Object.getOwnPropertyNames([1, 2, 3]);
 
     assert(names.length === 4);
-    assert(names[0] === '0');
-    assert(names[1] === '1');
-    assert(names[2] === '2');
-    assert(names[3] === 'length');
+    assert(names[0] === "0");
+    assert(names[1] === "1");
+    assert(names[2] === "2");
+    assert(names[3] === "length");
+
+    names = Object.getOwnPropertyNames({ foo: 1, bar: 2, baz: 3 });
+    assert(names.length === 3);
+    assert(names[0] === "foo");
+    assert(names[1] === "bar");
+    assert(names[2] === "baz");
 
     console.log("PASS");
 } catch (e) {