Ref T2009. Currently, lines don't get their "C123NL456" IDs set in the unified view. This is the major way that inlines are glued to changesets.

Simplify this rendering and bring it into the HTML renderer, then use it in the OneUp renderer.

• Interacted with side-by-side inlines (hovered, added, edited, deleted), saw unchanged behavior.
• Interacted with unified inlines. They still don't work, but the error that breaks them is deeper in the stack.