BuiltOutputProjectGroup target does not include runtimeconfig.json file

[rohit21agrawal]

@nguerrera @eerhardt

[rainersigwald]

I didn't know this thing existed until a couple of weeks ago (the Nugetizer folks are using it). Probably the best thing to do would be to add a target BeforeTargets="BuiltProjectOutputGroup" that emits to the same item that this target creates: https://github.com/Microsoft/msbuild/blob/99bd31a867a5509054ffddbebb37aad2c54aaee2/src/XMakeTasks/Microsoft.Common.CurrentVersion.targets#L5172-L5175

[dsplaisted]

What does BuiltOutputProjectGroup do? How is the BuiltProjectOutputGroupOutput item group used?