Support ".Ref" targeting packs and .NET Standard 2.1#2919

Merged

dsplaisted merged 10 commits intodotnet:release/3.0.1xxfrom

dsplaisted:use-targeting-pack

Feb 19, 2019

Commits on Feb 13, 2019

Support targeting .NET Standard 2.1
dsplaisted
committed

Commits on Feb 15, 2019

Apply code review feedback
dsplaisted
committed

Commits on Feb 18, 2019

Download runtime packs based on RuntimeIdentifiers property
dsplaisted
committed

Commits on Feb 19, 2019