Designer assemblies not loading for .NET Framework

[brianlagunas]

Describe the bug

When using the Behaviors NuGet package in Visual Studio, the design assemblies are not loaded for .NET Framework projects.

To Reproduce
Steps to reproduce the behavior:

1. Create a new WPF Application (.NET Framework)
2. Add the Behaviors NuGet
3. Create an EventTrigger
4. In the property grid, notice the properties are not grouped properly and there is no editor for the EventName property

Expected behavior
You should see this:

Reproduction Link
Download DesignTool-Issue.zip

@mgoertz-msft I think this is your area of expertise 😄

[brianlagunas]

The problem is that the Microsoft.Xaml.Behaviors.DesignTools.dll is not included in the .net462/design folder.

We just need to modify the dotnet pack to add the additional design assembly.