LibJS: Add property configuration transitions

Object.defineProperty() can now change the attributes of a property
already on the object. Internally this becomes a shape transition with
the TransitionType::Configure. Such transitions don't expand the
property storage capacity, but rather simply keep attributes up to date
when generating a property table.

Libraries/LibJS/Tests/Object.defineProperty.js

@@ -33,6 +33,14 @@ try {
         assert(e.name === "TypeError");
     }
 
+    Object.defineProperty(o, "baz", { value: 9, configurable: true, writable: false });
+    Object.defineProperty(o, "baz", { configurable: true, writable: true });
+
+    d = Object.getOwnPropertyDescriptor(o, "baz");
+    assert(d.configurable === true);
+    assert(d.writable === true);
+    assert(d.value === 9);
+
     console.log("PASS");
 } catch (e) {
     console.log(e)