RazorSDK does not compile against reference assemblies when CompileUsingReferenceAssemblies=true

[pranavkm]

Here's what Csc uses to calculate the assemblies to compile against: https://github.com/microsoft/msbuild/blob/e812790eabece155f9ea7cbc13d57ce1ad7bff19/src/Tasks/Microsoft.Common.CurrentVersion.targets#L2140-L2171. We need to change https://github.com/dotnet/aspnetcore-tooling/blob/master/src/Razor/src/Microsoft.NET.Sdk.Razor/build/netstandard2.0/Sdk.Razor.CurrentVersion.targets#L572

[pranavkm]

This should be resolved as part of the source generator effort.