feat(ecmascript): Implement Iterator functions that don't need a helper

[r58Playz]

Implements Iterator object, Iterator.prototype.every, Iterator.prototype.find, Iterator.prototype.reduce, Iterator.prototype.some, and Iterator.prototype.toArray.

Refactors set_default_global_bindings to use a macro.

[aapoalas]

Wow, amazing work! Thank you!

I found some places where we can improve, nothing major though. Mostly related to avoiding duplicate scoping and such. One outright bug in the reduce method as well, but this is absolutely great! Looking forward to getting this merged soon! <3

[aapoalas]

I fixed the lifetime issues (just more required unbinding that I'd forgotten about :D ) and the one nit I had about the error message.

Will merge once tests say everything is okay. Great work, thank you very much! <3