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 an editorial change in the ECMA-262 spec. See:
https://github.com/tc39/ecma262/commit/ff60140
In doing so, as the new name implies, callsites are updated to pass in
an IteratorRecord themselves, rather than an iterable value.
