Track support Gradients

[edgarfgp]

Adding to support for Gradients in:

• Xamarin Forms : https://docs.microsoft.com/en-us/xamarin/xamarin-forms/user-interface/brushes/gradient
• Maui https://docs.microsoft.com/en-us/dotnet/maui/user-interface/brushes/gradient

We need to make the background modifier accept Gradients.