Ref T8116. Partially scavenged from D14152. This roughs in a new Packages application for Arcanist extensions and third-party applications, and adds a "Publisher" object.
A "Publisher" represents an individual or entity who is publishing a package, like "Phacility". It's explicitly not necessarily the original author -- just the primary entity vouching for the safety of the code.
A publisher just has a name and a unique key for now. For example, Phacility might have "Phacility" and "phacility", respectively.
Unique keys are immutable, e.g., the package "phacility/arcanist" will always be exactly the same package by exactly the same publisher.
