UnconfiguredProject load in CPSPackageReferenceProjectProvider forces a C++ projects load from cache

[nkolev92]

https://github.com/NuGet/NuGet.Client/blob/9131f7118cf739f339ee22fed031c15f0b02128e/src/NuGet.Clients/NuGet.PackageManagement.VisualStudio/Projects/CpsPackageReferenceProjectProvider.cs#L97-L108 casts to IVsBrowseObjectContext which forces a project load in C++ project systems.

This is done at solution load time and it's not ideal as C++ tries to support PackageReference in native projects.
We don't need UnconfiguredProject at this time really.
We just need it when we install a package so we can delay this load.