Intersection type doesn't refine unions inside matching properties

[Reproducing using https://flow.org/try/](https://flow.org/try/#0C4TwDgpgBAshDO8CGBzaBeKBvAJk4SAXFALYCWAHhDgL5QBk2eBxWAUFFAGZkA2ErHv2IBGGmxriAxgHsAdvGBR5JBMjRRMXAK5ypwMvKgAKAbDWoIASmwcoZLiYgA6ZkmdDrtzuJpA)
```js
type Message = MessageEvent & {data: {
file: {file: File}
}}
onmessage = function (e: Message) {
if (e.data.file) {
// do stuff with File
}
}
```
## Expected
> :grinning:
## Actual
> property `file` Property not found in mixed