[whatwg/streams] Interesting edge case... queueMicrotask and desiredSize in start algorithm (Issue #1362)

jasnell created an issue (whatwg/streams#1362)

### What is the issue with the Streams Standard?

Take the following example...

```js
const rs = new ReadableStream({
  start(c) {
    queueMicrotask(() => {
      console.log('A:', c.desiredSize);
      c.enqueue('a');
      console.log('B', c.desiredSize);  // We've enqueued.. why is desiredsize unchanged?
    });
  },
  pull(c) {
    console.log('C', c.desiredSize);
    c.enqueue('b');
    console.log('D', c.desiredSize);
    c.close();
  }
}, { highWaterMark: 1 });

const reader = rs.getReader();
console.log(await reader.read());
console.log(await reader.read());
console.log(await reader.read());
```

Per the expected behavior of the queue and highWaterMark and desiredSize, what would you expect the value of `c.desiredSize` at position B? The answer is a bit surprising and all of the impls appear to agree... but the result is extremely counterintuitive...

```
A: 1
B 1
C 1
D 0
{ value: 'a', done: false }
{ value: 'b', done: false }
{ value: undefined, done: true }
jsnell@james-cloudflare-build:~/projects/cloudflare/edgeworker/deps/workerd$ deno ~/tmp/a.mjs
A: 1
B 1
C 1
D 0
{ value: "a", done: false }
{ value: "b", done: false }
{ value: undefined, done: true }
jsnell@james-cloudflare-build:~/projects/cloudflare/edgeworker/deps/workerd$ bun run ~/tmp/a.mjs
A: 1
B 1
C 1
D 0
{
  value: "a",
  done: false,
}
{
  value: "b",
  done: false,
}
{
  value: undefined,
  done: true,
}
```

Chrome also agrees with `B 1`

If we run the same code outside of the `queueMicrotask`, directly within `start` without the deferral, we get the result I think is more expected, `B 0` ... but it seems that enqueing within the `queueMicrotask` in this example is possibly exposing a spec bug.

@annevk @MattiasBuelens ... any ideas here?

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