Changes:
* Add a test project with simple unit tests for the shared framework
* Add root-level Directory.Build.props/targets files
* Cleanup .csproj files to reduce duplication
The MicrosoftNETPlatformLibrary property instructs the .NET Core SDK to treat a particular package as the shared framework platform. This affects how the SDK will trim references and publish output, determines how the runtimeconfig files are generated, and may affect how optimizations are preformed by other tools. In some installations of .NET Core, the ASP.NET Core shared framework is not available. This change adds properties to let the SDK determine on which platforms ASP.NET Core is enabled.
- Remove unnecessary tasks and scripts
- Ensure the KOREBUILD_DOTNET_* environment variables are preserved in the docker build context
- Other MSBuild cleanup of the targets