Summary:
Ref T13513. The on-hover-inline reticle has switched over to have cell-based behavior. Switch the on-hover-line-number reticle to use the same behavior.

Also, clean up the dirty/redraw loop slightly: we no longer need to dirty on resize, and we don't need to redraw if the range isn't actually dirty.

Test Plan: Highlighted lines and line ranges. Hovered over inlines.

Maniphest Tasks: T13513

Differential Revision: https://secure.phabricator.com/D21262