R1:616976a45c83

Make inline reticle code more general and robust

Summary:
Ref T2009. Currently, the code which draws the reticle is sort of implicitly hard-coded with some of the rules for the 2up view.

Instead, use general rules:

- Start selection at the next `<td />`.
- End selection at the rightmost adjacent `<td />`.

These rules work in all cases.

Test Plan:
- Activated reticle in 1up and 2up views by clicking line numbers and hovering over comments. It now draws correctly.
- Dragged over line ranges in…