Depends on D19677. Ref T13098. This gets enough of the new workflow/toolset stuff running to run arc liberate (without arguments) so that the new arc can bootstrap itself to continue development.
This change also moves some workflows which will be shared across toolsets (shell completion, versions, help, aliases) out of being arc-specific, to varying degrees of success. These workflows will need to be revisited and cleaned up so they work properly. They mostly fatal when run right now.
The Conduit flags have moved to the new arc parent workflow, but they'll likely move to some kind of support object so my-company-thing megadiff can accept Conduit flags. This is a more involved change, however.