Fix several visual issues with find result highlighting:
- Reduce width of scrollbar tickmarks to match new, narrower custom-themed
scrollbars (should also look better on Mac, where the tickmarks were already
too wide)
- Fix bug where showing/hiding a bottom panel didn't update the positioning
of scrollbar tickmarks
- Results that span multiple tokens showed little orange dots in the text
highlight between tokens (due to repeated corner rounding). There are still
faint lines between tokens (due to box-shadow), but they're much fainter.
Merge pull request #6478 from adobe/pflynn/find-highlighting-tweaks

Fix several visual issues with find result highlighting: