SixLabors.ImageSharp 3.0 breaks compatibility

[ASPePeX]

SixLabors.ImageSharp 3.0 dropped support for .NET Standard. Since we use it F.B.Core using it means dropping .NET Standard support for the whole engine, except for maybe F.Math.Core.

https://www.nuget.org/packages/SixLabors.ImageSharp/#supportedframeworks-body-tab

IMO this isn't a problem since the net[X].0 implementations are now the base imp that .NET Standard was a few years ago. We could switch to net6 and net7 and would be still compatible with all supported frameworks.

[ASPePeX]

Android is a problem. Needs alternatives to Xamarin.