ArrayIterator and RegExpStringIterator are no longer reentrant

[anba]

#2045 made ArrayIterator and RegExpStringIterator no longer reentrant, which doesn't match implementations.

The following test case should throw a TypeError per the current spec, but does throw "unreachable" in all engines.

let obj = {
  get 0() {
    it.next(); // <-- Should throw a TypeError per current spec!
  },
  get 1() {
    throw "unreachable"; // <-- Unreachable per current spec.
  },
  length: 2,
};
let it = Array.prototype.values.call(obj);
[...it];

Relevant steps:

• %ArrayIteratorPrototype%.next ( ) calls GeneratorResume.
  • GeneratorResume, performs generator.[[GeneratorState]] to executing.
    • Side-effects in the ArrayIterator abstract closure call %ArrayIteratorPrototype%.next.
      • GeneratorResume calls GeneratorValidate.
        • GeneratorValidate throws a TypeError because state is executing.