[RFC] emit_async_iterator_return_close() added for async of

[sadhbh-c0d3]

• Added emit_async_iterator_return_close()

This is to fix discrepancy between Quickjs and V8 behaviour when Async Iterator is finalised.

Below is the test that can be applied to confirm behaviour without this change (after this change QuickJS behaviour is identical to V8).

let flag = false;
const it = {
  i: 0,
  async next() { return this.i++ ? { done: true } : { value: 1, done: false }; },
  async return() {
    await 0;
    flag = true;
    return { done: true };
  },
  [Symbol.asyncIterator]() { return this; }
};

(async () => {
  for await (const x of it) break;
  console.log(flag);                     //< QuickJS: false, Node: true
  await Promise.resolve();
  asyncIteratorCloseObserved.push(flag); //< QuickJS: true, Node: true
})();