Await async iterator return() when a for-await loop breaks

[littledivy]

When a for await loop is exited via break, the async iterator's return() method is called but its result is not awaited. Per spec, AsyncIteratorClose performs Await(Call(return, iterator)), so code after the loop must not run until that promise settles. Only async generators awaited the close; a plain async function used the synchronous close path.

const it = { [Symbol.asyncIterator]() { let i = 0; return {
  next() { return Promise.resolve({ value: i++, done: false }); },
  return() { log.push("return"); return Promise.resolve().then(() => log.push("resolved")); },
}; } };
for await (const x of it) break;
log.push("after");

step order	before	after
return called	yes	yes
return() promise awaited	no	yes
log	return, after	return, resolved, after

The break/loop close now routes async iterators through a shared helper that calls return() and awaits it, and skips the call when the iterator was already closed on normal completion.

Disclaimer: This is an AI-assisted patch from the v8x project.