R1:3ea47d967ab7

Allow monogrammed objects to be parsed from the `arc` command line in "Reviewers" and similar fields

Summary:
Ref T10939. This allows the CLI to parse reviewers and subscribers like this:

```Reviewers: epriestley, O123 Some Package Name```

The rule goes:

- If a reviewer or subscriber starts with a monogram (like `X111`), just look that up and ignore everything until the next comma.
- Otherwise, split it on spaces and look up each part.

This means that these are valid:

```
alincoln htaft
alincoln…