On X11 we already had to wait as window managers might scroll windows
in. On macOS we also waited - albeit a bit shorter - also because
screens scroll in slowly.
We didn't wait on Windows, and on Windows the test is quite flaky.
Attempting to make it run stably by waiting for long enough so that all
paint events are flushed to the screen.
As a drive-by, break some overly long lines.
Task-number: QTBUG-100412
Pick-to: 6.3
Change-Id: I49b1e447aced2fe1af3c5d30b514f8df3cc1813c
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
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