Virtual scroll buggy for large json file

- Large json files display large file warning (expected)
- User can click to view entire file, which should enable virtual scrolling (works)
- Scroll should render part by part. Currently this is jittery and gets stuck (scrolling is blocked)

No file, test, or entry point is named. Start by locating the virtual-scrolling implementation used when viewing large JSON files; the work is done when scrolling renders incrementally without jitter or becoming blocked.

Written by the indexing model from the issue text.