Restore Directory.Build.props directly

[GeraudFabien]

When you create a dockerfile you :

• Move the csproj
• Restore
• Move all files
• ...

https://stackoverflow.com/questions/53460002/how-to-use-dotnet-restore-properly-in-dockerfile
It may be easier and more explicit if we do that instead:

• Move the Directory.Build.props
• Restore
• Move all files
• ...