The [NSWidow windowNumberAtPoint:belowWindowWithWindowNumber] API has issues
with sometimes being out of sync with the window server, resulting in failing
to hit test windows that we know are there.
This has manifested in flakeyness in our tests, for example in tst_QWindow's
testsInputEvents: http://testresults.qt.io/grafana/goto/YNGj7TgIg
A workaround is to call [NSWindow windowNumbersWithOptions:0] to force a sync,
but we might as well use the more modern block based API to iterate our own
windows in Z-order. This API seems to do the required sync on our behalf,
or at least doesn't operate on stale data.
The logic has been otherwise kept as is, including treating non-top-level
windows as candidates for hit testing, which seems strange for a function
named topLevelAt(). This is to be investigated further.
Task-number: QTBUG-108402
Task-number: QTBUG-115945
Pick-to: 6.6 6.5
Change-Id: I5599881c381a0a673d262e4b9585e2c6798c9810
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>
108d2e4486