reorder the Iterator.* and Iterator.prototype.* sections

The spec's convention is:
when you have a set of sections that define the properties of some intrinsic object,
first do the properties whose keys are strings, in alphabetical order,
then do the properties whose keys are symbols, in alphabetical order.

(The only exception is in "Properties of the RegExp Prototype Object",
where the symbol-keyed-properties are interleaved with the string-keyed-properties.)