With multi targeted projects, NuGet should read the target framework related information from the inner build.

[nkolev92]

Currently in command line scenarios NuGet reads the target framework information in the outer build.
That is incorrect because the the contract is that we should depend on on TargetFrameworkIdentifier and the like properties.
We do that here: https://github.com/NuGet/NuGet.Client/blob/bd482514a87a0085f8eb8603842ee1cb3ca5f277/src/NuGet.Core/NuGet.Build.Tasks/NuGet.targets#L500-L526

This task is a blocker for #5154.

An incomplete list of things that need done are:

• In command line scenarios, read the framework in the inner build (this should allow us to read OS Version for example).
• In VS scenarios, modify the VSSOlutionREstoreService to read the information from the properties back instead of the TargetFrameworks value.
• Reflect all of the changes in the assets file (not sure if we'll need any).

• Commandline restore (nuget.exe, msbuild.exe dotnet.exe).
• Commandline Static Graph restore.
• VS restore