Follow-up to #4658 (review)
- Replace spelled out numbers with numerics
- Update grouped nav description to align with image
- Update two-level/three-level nav description and headers
- Fly-out > Flyout? React docs call it Flyout (confirm which is right)
- Remove specifics in secondary horizontal nav description, which aren’t relevant to the image
- For secondary horizontal nav, add subheadings for each image (vertical vs horizontal primary)
Follow-up to #4658 (review)