Add ViewCell Analyzer for Xamarin.Forms

[mrlacey]

Don't put a ViewCell in a Carousel

https://docs.microsoft.com/en-us/xamarin/xamarin-forms/user-interface/carouselview/populate-data

When using CarouselView, never set the root element of your DataTemplate objects to a ViewCell. This will result in an exception being thrown because CarouselView has no concept of cells.

This is a follow-on from #411 but wasn't implemented there as doing so would mean adding this analysis for the Carousel.
Consider doing when can view parents/containers from within an analyzer.

Low priority due to low use of ViewCell