LPS-46221 Wrap autocomplete.js module to prevent leaking vars to global

Hey @natecavanaugh,

I've added a commit to prevent leaking the vars to global. Sorry about that, I assumed the CKEditor ScriptLoader was doing it for us :(

About the errors you were seeing:
__`this[sourceSetter] is not a function`:__ This is why we need to introduce the fix in [AUI-1290](https://issues.liferay.com/browse/AUI-1290)

__`Uncaught TypeError: Cannot read property 'getDocument' of null`:__ If you still see this, it usually means we're failing to find some ascendant when getting the DOM walker for some nodes from CKEditor. Were you seeing this inside some formatted code, or simply writing inside the editor?

In addition, I've tested this also after applying the new CKEditor version on https://github.com/natecavanaugh/liferay-portal/pull/2416 and everything seems to be working as expected. 

Please, let me know if you still have problems with this.

Thanks!