Ensure WPF tests without the System.Runtime.Serialization.Formatters package

[ericstj]

The default behavior of System.Runtime.Serialization.Formatters changed in .NET 9 to throw always.

To keep WPF's tests working we added a reference to the compat package for this.

WPF should add a test that validates the throwing behavior without this package. That would need to be a separate assembly.