Add Iterators and the for..of loop

[Elchi3]

(For Iterator methods, see #1656)

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for...of
https://chromestatus.com/feature/4696563918045184

Using compute_from here, as I think the for_of key is the most relevant data point for this one.

There are also iterator symbols on many JS builtins and these could belong to this feature (e.g. javascript.builtins.String.@@iterator and many more). Array has its own feature: https://github.com/web-platform-dx/web-features/blob/main/features/array-iterators.yml. Not sure if this should rather all be here or if we want this to be separate for each builtin.

[autonome]

There are also iterator symbols on many JS builtins and these could belong to this feature (e.g. javascript.builtins.String.@@iterator and many more). Array has its own feature: https://github.com/web-platform-dx/web-features/blob/main/features/array-iterators.yml. Not sure if this should rather all be here or if we want this to be separate for each builtin.

I think is good how you've done this as the generic + usage (for...of), and leaving instance-specific iterators w/ their instances.

Spec authors and implementers may think of something like iterableness as group that crosses instances of it, but developers think on the instance/usage level. Eg, imagine you're looking up if something is iterable - developer would go to the something docs for that.

Requests complete