Turn on anti-aliasing, and update screenshot.
The example is still not great and under-documented, but at least it
doesn't look horrible anymore.
Pick-to: 6.7 6.6
Task-number: QTBUG-120291
Change-Id: Ie709cb51d64c535d7cd0aa1451b3c5bb901324cb
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>