arcade: Microsoft.DotNet.Arcade.SDK does not import publish targets

Using <Project Sdk="Microsoft.DotNet.Arcade.Sdk"> does not import any of the targets related to publish.

I’d like to be able to use the logic mentioned in https://github.com/dotnet/arcade/blob/master/Documentation/CorePackages/Publishing.md, both:

• the “Publish” target from https://github.com/dotnet/arcade/blob/master/src/Microsoft.DotNet.Arcade.Sdk/tools/Publish.proj#L33, and
• the related tasks that it imports from https://github.com/dotnet/arcade/blob/master/src/Microsoft.DotNet.Build.Tasks.Feed/build/Microsoft.DotNet.Build.Tasks.Feed.targets

The eng scripts call publish by running msbuild on build.proj, which calls msbuild on publish.proj. However, for projects that use the “Project Sdk” syntax, it doesn’t get imported. There also aren’t any convenient properties defined that would make manually importing the target files easy (I would have to write logic to detect the arcade toolset installation directory).

This is especially important for helping arcade onboarding, as it will make it easier to write part of our build logic (the publishing logic) against arcade before the whole repo has moved to using the eng/* scripts.