QDockWidget: Unsetting DockWidgetFeature::DockWidgetMovable has no effect for floating dock widgets

Currently, floating the widget will allow the user to move the widget - even if we try and restrict this via setFeatures(features() & ~QDockWidget::DockWidgetFeature::DockWidgetMovable).

That is. docks can be redocked into a different area after made floating.

But is this appropriate if we really don't want to allow the user to move the dock widgets around?

So we could either:

A) Change Line 925 in QDockWidget.cpp to:

state->ctrlDrag = (hasFeature(this, QDockWidget::DockWidgetFloatable) && event->modifiers() & Qt::ControlModifier) ||
(!hasFeature(this, QDockWidget::DockWidgetMovable) && q->isFloating());

 B) Add an extra DockWidgetFeature to allow this move when floating behaviour to be enabled/disabled.