R1:53a678c56823

Improve documentation and tooling around autoclose

Summary:
Fixes T4767. I believe 80% of this was actually caused by the author issue fixed in T5771, but this should help make the other 20% debuggable.

- Record why we didn't autoclose a commit when we process it.
- Show branch autoclose status in the main branch table.
- Show commit autoclose status on the edit screen.
- Add documentation about how to find these statuses and what they mean.

Test Plan:
- Read documentation.
- Viewed branches…