Allow ArrayList to be subscriptable

[bfbenf]

Issue: The sub classes of Collection (List / Array List) do not support [0] etc when they do on a production instance. It's also very hard to patch the prototype like you can for other things.

Possible Solution: Introduce some sort Proxy or inherit from Array to allow us to test code with [0] and still use the collection methods.

[SGD1953]

You could try something like class Collection extends Array { and then slightly refactor it to leverage this.push(elem) for add etc. If that works, a PR would be neat.