Move commit attachment to a separate CLI command
Summary:
Ref T9319. See D14967. As before, this is making a deeply-buried, complex operation easier to test by providing a CLI command.
This adds `bin/differential attach-commit rXnnnn Dnnnn` to pretend that `rXnnnn` was just committed and matched `Dnnnn`.
Test Plan:
- Ran `bin/differential attach-commit X Y` for several different values, saw updates in the UI.
- Faked the message parser to make sure stuff still worked there.
Reviewers: chad
Reviewed By: chad
Maniphest Tasks: T9319
Differential Revision: https://secure.phabricator.com/D14968