Need to add plain @(Reference) information to the .deps.json file

[eerhardt]

On Desktop projects (and technically .NET Core projects now in the MSBuild world), it is possible to have normal references to assemblies. Specifically references to "Reference Assemblies" in the .NET Framework.

We need to add these assemblies to the .deps.json file. In project.json based projects, for desktop specifically, these kinds of references only got added to "CompilationAssemblies", there were no runtime assets for them, since it assumed the runtime library is already present. Thus they should only be added to the "compile" libraries in the deps.json file.

See https://github.com/dotnet/cli/blob/1278e9d6bf35500e9672fe3f53125df1d08717d8/src/Microsoft.DotNet.ProjectModel/Compilation/LibraryExporter.cs#L389-L402

Also, when we do this, the project.json based CLI would use the relative path from the "Reference Assemblies" folder (C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework) in the path in the .deps.json file. See https://github.com/dotnet/cli/blob/1278e9d6bf35500e9672fe3f53125df1d08717d8/src/Microsoft.DotNet.ProjectModel/DependencyContextBuilder.cs#L221-L238

[eerhardt]

Along with this, we should think about how plain @(Reference) items to loose assemblies on disk should work on both desktop and .NET Core. Or if we should block it in certain cases.