Support for "classic" .NET project

We are running an on-premises devops server which creates nuget packages from our modules. All projects are "classic" .NET projects (targeting 4.7.2). In order to enable source link support we added the following packages to our modules:

```



```
Furthermore the project files (*.csproj) were modified like this:

```

...............
true
true

```

```



```

In another repository we have projects with references to these NuGet packages. When running in a debugger the symbols are loaded but the sources are not found. So we are a little bit lost here. For me it is not really clear what steps have to be done in order to use SourceLink support in "classic" .NET projects. By the way the debug information (pdb) will be put to a network share during the builds.