Cross-Client no-op for legacy package reference

[nkolev92]

The secondary target of this feature is to unify the restore behavior among all our clients.
One can restore with NuGet.exe, open VS, and then auto-restore no-ops. When that, the user can build use msbuild /t:restore and that would no-op as well.

At this point that's not the case.
The dg spec generated for msbuild/nuget.exe/dotnet.exe case is not the same as the one generated by VS. Some of those inconsistencies have been resolved, while others haven't.

Here's a table of the presumed behavior (meaning, as far as we know, there might be some crazy scenarios in which this breaks, and when encountered, we'll want to fix them.

Project Model	NuGet.Exe & VS Client	NuGet.exe & dotnet.exe	NuGet.exe & MsBuild	VS Client & dotnet.exe	VS Client & MsBuild	MsBuild & dotnet.exe
.NET Core - SDK based projects	Consistent	Consistent.	Consistent.	Consistent.	Consistent.	Consistent.
Legacy Package Reference projects	Inconsistent.	Consistent.	Consistent.	Inconsistent.	Consistent.	Inconsistent.
Project.Json	Inconsistent	Consistent.	Consistent.	Inconsistent.	Inconsistent.	Consistent.