System.ServiceModel.Federation package doesn't support .NET Standard in 8.1.0

[wrall]

Describe the bug
Through version 4.10.3, System.ServiceModel.Federation package supported a netstandard2.0 target, allowing it to be used by .NET Framework and .NET Core targets alike. There is no such target in the version 8.1.0 which was intended to reintroduce support for .NET Standard.

To Reproduce

1. Create a project that targets net472, net6.0, net8.0.
2. Add System.ServiceModel.Federation package reference.
3. Add code that uses System.ServiceModel.Federation classes.

Expected behavior
Project compiles/builds for all net472, net6.0, net8.0 targets.