Stop worrying about tiny OOMs. Work towards #20449.
While going through these, I also changed the function signature in many
places where returning ThrowCompletionOr<T> is no longer necessary.
Rather than splitting the Iterator type and its AOs into two files,
let's combine them into one file to match every other JS runtime object
that we have.
This is in preparation of implementing %IteratorHelperPrototype%.return.
That will invoke GeneratorResumeAbrupt, which will execute the generator
with an abrupt completion. At that time, we must take care to close the
current inner iterator.
This is required for %IteratorHelperPrototype%.return, which needs to
operate on the internal slots of the base GeneratorObject. Doing so also
provides us with the appropriate VM to be used in invocations to the
overridden IteratorHelper::execute.
This uses a new Iterator type called IteratorHelper. This does not
implement IteratorHelper.prototype.return as that relies on generator
objects (i.e. the internal slots of JS::GeneratorObject), which are not
hooked up here.
