Document an exhaustive list of packages shipped in or used by a given version of the .NET SDK

[baronfel]

Users that maintain package feed caches need to know what to populate on release day, so we should have a machine-readable list of all packages the SDK might grab, either as Package Downloads or Implicit Package References.

Categories of packages that should be included (not exhaustive):

• Runtimes
• AppHosts
• SingleFileHosts
• ILLink and related tasks

Once this machine-readable list is generated it should be a release artifact and should be used to power:

• automated linkages for the release.jsons
• human-readable markdown documentation in the release notes and detailed developer/administrator documentation.