setFloating() called on the 2nd last dock widget in a floating tab
didn't cause reparenting to the main window. The dock widget remained
parented to a QDockWidgetGroupWindow, while no longer being part of
floating tabs. The QDockWidgetGroupWindow would therefore have only
one tab, which is an inconsistent state and causes crashes.
Factor out the implementation of setFloating() to a new
QDockWidgetPrivate::setFloating(). Reparent to the main window, if
the dock widget is part of floating tabs.
Add test functionality in tst_QDockWidget::setFloating().
Turn createFloatingTabs() into a macro, in order to QSKIP() in the test
function's scope.
Fixes: QTBUG-122394
Pick-to: 6.7 6.5
Change-Id: I3719785f310b131446cdea908f09b7195c992b3e
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
a910daf526