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.
Task-number: QTBUG-120291
Change-Id: Ie709cb51d64c535d7cd0aa1451b3c5bb901324cb
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>
(cherry picked from commit 2b9d021ba5487f7f5f67b958a17160c4cf468561)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit d8b113f46f11dd6d7229df0cb58f56dccfc70eb5)