Pack symbols should validate that the symbols files are portable

[jozefizso]

NuGet product used: nuget.exe

NuGet version: 5.0.2.5988

VS version: 2017

OS version: Windows 10 2004

Detailed repro steps so we can see the same problem

1. Compile .NET project with debug symbols enables
2. Create nuget package with modern snupkg format
3. Push the package to nuget.org
4. Symbol package validation fails

Expected behavior

Nuget.exe should fail to push a package to nuget.org if the snupkg packages does not contain correct symbol files. Once the main package is pushed, it is impossible to fix symbol packages for a release and the main package is immutable.

Nuget.exe should also warn about incorrect PDB format when creating the snupkg files.

[donnie-msft]

What sort of validation error were you seeing? Was nuget.org still validating the previous push? I wrote an issue here which describes the behavior: NuGet/NuGetGallery#7681

The issue I see with validating on push is, how will push know which symbols you intend to include, and how does it know what the server will accept?
//cc @zkat

[jozefizso]

Validation error: The uploaded symbols package contains one or more pdbs that are not portable.

It is clear which PDB format is supported by snupkg files. Either nuget.org should wait with publishing packages till symbols are validated, or it can detect this trivial error when generating packages.