[Enhancement] tvOS support

[VladislavAntonyuk]

Summary

Add support for tvOS
I saw a branch in XF repository. I think it would be nice if you allow community to support the new platform.

API Changes

I don't know what is implemented so far, but we can start from adding must have controls: Page, View, Layouts, Button, Label, Entry, Image. It should cover mostly apps requirements.

Intended Use Case

Create app for tvOS in a few minutes. Simple migration of already existed app.

Xamarin Community Toolkit and Xamarin Essentials have tvOS as target framework.