When a floating dockwidget's title changes, it is rendered as a
window title. When the title changes while floating, the change will be
reverted to the pre-change title when the dockwidget is docked again.
This patch explicitly propagates the window title, if it has been
programmatically changed while the dock widget is floating.
It adds test functionality in tst_QDockWidget::floatingTabs().
Fixes: QTBUG-113591
Pick-to: 6.6 6.5
Change-Id: I96fa69fb27ad1a85f4ea9ce44c0a22290259fca6
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
c153066baa