[whatwg/streams] Internal promises need to be handled before they reject (#1139)

At the moment the spec takes care of rejected promises in the following way:

1. Create a rejected promise
2. Mark the promise as handled

or

1. Reject the promise
2. Mark the promise as handled

This happens in [WritableStreamDefaultWriterEnsureClosedPromiseRejected](https://streams.spec.whatwg.org/#writable-stream-default-writer-ensure-closed-promise-rejected) for instance.

However, according to the [Promises spec](https://tc39.es/ecma262/multipage/control-abstraction-objects.html#sec-host-promise-rejection-tracker) the UA needs to do checks the moment a Promise rejects. So if you mark a promise as handled after it rejects, it is already too late.

This can be seen from running the following in the console in Chromium:
```js
ws = new WritableStream();
writer = ws.getWriter();
writer.releaseLock();
```

If 'Pause on exceptions' is enabled, script excecution gets paused twice. Once for the `ready` promise and once for the `closed` promise.

The Chromium issue for this is tracked in https://crbug.com/1132506

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