There're two errors in scrollbar markers in the presence of folded code: 1. Some markers are not displayed (when the marked row numbers are greater than the total displayed rows count after folding). 2. Code folding / unfolding doesn't trigger markers repainting. This PR fixes both problems. Release Notes: - Fixed scrollbar markers for folded code. The second problem (markers are repainted after I move the cursor, not after folding): https://github.com/zed-industries/zed/assets/2101250/57ed563d-186d-4497-98ab-d4f946416726