Reparenting QTabWidget with a native window tab can cause crash

When a native window widget (child of another top-level window) is added as a tab to QTabWidget and then the QTabWidget is reparented to a new top-level window, the widget's top-level system extra window is not reparented to the new top-level window as expected. Due to this, when the old top-level window goes out of scope, the widget's extra window is destroyed and further access to the widget's window handle would result in a crash.

Steps to Reproduce:

1. Create a QWidget as a native window and parent it to another top-level native window.
2. Add QWidget as a tab to a QTabWidget using QTabWidget::addTab
3. Reparent the QTabWidget to a new top-level window aka newTLW using QWidget::setParent.
4. Destroy the old top-level window.
5. QWidget's top-level system extra window would be destroyed and the QWidget would contain a dangling pointer.

Expected Behavior: 
The QWidget's top-level system extra window should be reparented to the new top-level window when the QTabWidget is reparented.

Actual Behavior:
When the old top-level window goes out of scope, child windows associated with the old top-level window's extra are destroyed, including the system extra window. This leaves them QWidget with a dangling extra window pointer. Any future access to this window handle would result in a crash.

Additional Notes
A simple reproducer app is attached QTBUG-122747.zip .