Implement a function mapAsyncLimit(items, fn, size) that maps over an array with an asynchronous function but limits the number of concurrently running async tasks.

The function should:

• Accept an array of items.
• Accept an async mapping function fn that returns a Promise.
• Accept an optional concurrency limit size. If not provided, all tasks can run concurrently.
• Return a Promise that resolves to an array of mapped results in the original order.

Example

async function fetchUpperCase(q) {
  return q.toUpperCase();
}

const results = await mapAsyncLimit(['foo', 'bar', 'qux'], fetchUpperCase, 2);
console.log(results); // ['FOO', 'BAR', 'QUX']