This MR does several things as a followup to
https://invent.kde.org/plasma/plasma-mobile/-/merge_requests/748:
- Use the word "lock" instead of "sleep" since we are locking the
device, not putting it to sleep
- Simplify usage by using existing MouseAreas instead of including our
own for this feature (I encountered several focus captures in folio that prevented the
SwipeArea from getting events)
