Visual Studio Restore does not properly pick up package references transitively for project references outside the solution

[dfederm]

When restoring in VS, if a project has a project reference outside the solution, and that project outside the solution has a PackageReference, the first project (in the sln) will not end up with that package in it's project.assets.json. It works properly when using MSBuild /t:Restore

Repro steps:

1. Create a project A with a package reference to a package X
2. Create a project B with a package reference to package Y
3. Add a project reference from project A to project B
4. Create a solution with just project A
5. Do a restore in VS
6. Observe that project A's project.assets.json is missing package Y
7. From the command line and do an "msbuild /t:Restore" on project A
8. Observe that project A's project.assets.json is properly has package Y

[nkolev92]

This is by design, because NuGet depends on the project system.

Duplicate of #5820 and dotnet/project-system#2759

Please track the open issue in the project system repo.