[app] Enumerator in Chakra engine mode

[gnh1201]

Summary

As mentioned in the previous issue #30, Enumerator is non-standard, so it is not supported in Chakra mode, which supports ES5-level syntax. When WelsonJS is in Chakra mode, it should be automatically changed to use Iterator or Generator.

Related issues

• [lib/std] [polyfill] Enumerator.prototype.toArray() #30
• [app] Transpiling ES6 generator functions #75