[XI] doesn't support QuickLook extensions

I am porting [swift sample](https://developer.apple.com/documentation/uikit/view_controllers/building_an_app_based_on_the_document_browser_view_controller?preferredLanguage=occ) into the Xamarin and found that XI doesn't support QuickLook extensions.

### Steps to Reproduce

1. Download a [sample](https://github.com/xamarin/private-samples/tree/particles/ios11/Particles)
2. Run it
3. Create an internal document and save it ('Done' button)

### Expected Behavior
`QLThumbnailProvider` implementation is invoked and thumbnail is created


### Actual Behavior
There is default icon and no additional call


### Environment

1. VSfM
https://gist.github.com/mykyta-bondarenko-gl/56bb56c36608563c29d56040a0e55252

### Build Logs

1. Build Output
https://gist.github.com/mykyta-bondarenko-gl/2ed4831f94368b3a00054b0c0c87ff52

### Example Project

[Particles](https://github.com/xamarin/private-samples/tree/particles/ios11/Particles)