WIP es7 compliant contains

- [x] es7 polyfil for contains
- [ ] get review on the poly

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- [ ] make enumerable stuff work correctly (ideally without lots of duplication)
- [ ] transition SHIM_ES5 to SHIM_ESNEXT

I think this detail is great, but I don't think this level of fidelity is what we need here. Browser sure, but I think we will only cover the reasonable paths.