Remove dependency on System.Json for net6.0

[akoeplinger]

The System.Json nuget package is deprecated (note: this is a different package than System.Text.Json) and will cause issues when consumed from .NET6-based Xamarin apps.

The reason is that the package ships with _._ entries for the legacy Xamarin TFMs which will be pulled in via NuGet compatibility fallbacks, however there is no System.Json assembly in the net6.0 shared framework (see dotnet/designs#222 for some lengthy discussion).

To fix the issue you'll need to multi-targetting to net6.0 and remove the dependency on System.Json there.

/cc @jeromelaban

[carldebilly]

System.Json is used by the Uno's Lottie Add-in to update the json document with custom resources (mostly colors). System.Text.Json can't be used because its JsonDocument is read-only and it seems there's no efficient way to update a json document with it.

On Android, there's a dependency to Newtonsoft's Json.NET because there's a bug in LottieXamarin for Android.

[jeromelaban]

Thanks for the update @akoeplinger!

We're still looking at integrating with .NET 6, and we hope that Preview 5 will help us move forward. The dependency on System.Json is the least of the problems (we could pull in the whole System.Json code as a workaround), as I'm not sure if the dependency on https://github.com/Baseflow/LottieXamarin will work on .NET 6 anyways.

GitHub

Baseflow/LottieXamarin

Render After Effects animations natively on Android, iOS, MacOS and TvOS for Xamarin - Baseflow/LottieXamarin