Templating dependency is not AOT friendly

[JeremyKuhne]

There are two existing issues that capture this:

dotnet/templating#1756
dotnet/templating#9193

The template engine needs moved from NewtonSoft.Json to System.Text.Json and the assemblies need marked as <IsAotCompatible>true</IsAotCompatible> when building for .NET core runtimes. That will likely entail addressing AOT/Trim warnings that pop up.