R1:f21f1d8ab9e9

Update the diff table of contents to use hierarchical views and edit distance renames

Summary:
Ref T13520. Generally, make the table of contents look and more like the paths panel:

- Show a hierarchy, with compression for single-sibling children.
- Use the same icons, instead of "M D" and "(img)" stuff.
- Use EditDistanceMatrix to do a piece-by-piece diff of paths changes.
- Show path changes within the path list.

I'm not entirely sold on this, but it was complicated to write and I've never…