R1:9abc16df4df5

Give Owners packages the "O" monogram

Summary:
Ref T10939. This isn't ideal because it's easy to confuse with zero ("O" vs "0") but I think this will mostly be read-only so it's probably one of the least-bad uses we could make of "O". We haven't really gotten into trouble with "I" (vs "1") for initiatives. Still, open to better ideas.

The goal here is to allow commit messages to include packages in some reasonable way, like `Reviewers: O123 Package Name, epriestley, alincoln`. The parser will ignore the…