Items with `required` properties cannot be used inside a `Loader`

Using a component with `required` properties inside a `Loader` and using a `Binding

` results in:
```
Required property someProp was not initialized
```

There currently does not seem to be a declarative way to use such component inside a `Loader`. Considering how the `required` keyword can be used to make components re-usable, and the fact that `Loader` has use cases with no other alternatives, this limitation of `Loader` reduces the re-usability of such components. So for example if you are using a library that has been designed to be safe and re-usable using the `required` keyword (rightly so), you would not be able to use purely declarative QML and the `Loader` component.

An imperative alternative would be to use `setSource` in the `Loader`.