Building an app with PreserveCompilationContext=true causes files from the shared runtime to be copied to bin\refs directory

[pranavkm]

This is a regression (?) in 2.1.0-preview2 sdk. Repro steps:

1. Acquire preview1 Sdk - https://www.microsoft.com/net/download/dotnet-core/sdk-2.1.300-preview1
2. dotnet new mvc
3. dotnet build

Examine the bin\Debug\netcoreapp2.1 directory and notice all it has is the app's binaries.

4. Clean the bin directory and run dotnet build using the preview2 Sdk (I used 2.1.300-preview2-008367)

The bin directory has a refs directory that contains 300+ files from shared runtimes.

[pranavkm]

_CopyReferenceOnlyAssembliesForBuild uses _ReferenceAssemblies as input for files to copy. Between preview1 and preview2, NuGetSourceType is no longer being set which causes package and runtime refs files to get copied to the bin directory.

Preview1	Preview2

[livarcocc]

@nguerrera caused by your changes?

[nguerrera]

Yes. I will fix this.

[pranavkm]

Is there a CLI available that contains this fix? Just like to verify this fixes Mvc scenarios e2e.

[nguerrera]

@pranavkm I don't think so unless there are already RC prodcon builds happening: cc @mmitche.

[mmitche]

There are, but nothing through CLI yet.