Summary of the new feature/enhancement

Currently the .csproj files for build reference assemblies are generated on-the-fly (the content is kept in a resource.psd1 file as templates).
We need a way to update the version of nuget packages referenced by those .csproj files, and the proposal is to have the .csproj files checked in, and then we can use the DependBot to manage the version of nuget packages referenced by those .csproj files.

Also, the generated SDK nuget packages are currently declared as netstandard2.0. We should change it to netcoreapp2.1 as the runtime libraries are netcoreapp2.1 specific.