[automated] Merge branch 'release/3.0' => 'release/3.1' (dotnet/Extensions#2748)

[automated] Merge branch 'release/3.0' => 'release/3.1' (dotnet/Extensions#2748)

* [release/3.0] Update dependencies from dotnet/core-setup (dotnet/Extensions#2719)

* Update dependencies from https://github.com/dotnet/core-setup build 20191126.03

- Microsoft.NETCore.App.Runtime.win-x64 - 3.0.2-servicing-19576-03

* Update dependencies from https://github.com/dotnet/core-setup build 20191126.05

- Microsoft.NETCore.App.Runtime.win-x64 - 3.0.2-servicing-19576-05

* Update dependencies from https://github.com/dotnet/core-setup build 20191126.08

- Microsoft.NETCore.App.Runtime.win-x64 - 3.0.2-servicing-19576-08

Dependency coherency updates

- Microsoft.NETCore.Platforms - 3.0.1-servicing.19576.7 (parent: Microsoft.NETCore.App.Runtime.win-x64)

* Update dependencies from https://github.com/dotnet/arcade build 20191127.5 (dotnet/Extensions#2729)

- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19577.5
- Microsoft.DotNet.GenAPI - 1.0.0-beta.19577.5
- Microsoft.DotNet.Helix.Sdk - 2.0.0-beta.19577.5

* Build implementation projects against ref assemblies

* Add explicit references in tests, where needed

Commit migrated from https://github.com/dotnet/Extensions/commit/d40e21ccc14908a054b2181b1d6aeb22c49c630d