FR: Implement JJ `run`

[PhilipMetzger]

This is the tracking issue for run, mostly for myself.

The design doc is available here (Google Docs) and here (docs/design).

Related to #405

• Add a barebones run command, which is hidden.
• Move the design doc from Google Docs to docs/design.
• Add the VFS integration point, for EdenFS and CitC.
• Implement the worker interface for the Git backend.
• Add a beautiful TUI with superconsole, based on @arxanas suggestion in On `jj run` #1486.

this should establish the base features of run.

And to add, here's a simple wishlist based on Discord conversations:

• Add run --bisect, to support a git bisect -x like workflow based on git-branchless's git test.¹
• Supporting bayesian based bisection ²
• Partially exposing the underlying repo, for the default backend with something like --files [PATHS]

Footnotes

1. My suggestion in Discord ↩

2. A suggestion from @thoughtpolice in Discord ↩

[arxanas]

The scm-bisect crate contains bisection logic already. For git run --bisect, it would be nice if we could centralize logic into scm-bisect so that other version control systems could potentially use it.