Regression: Drag and drop no longer works in Qt 4.8.3/Designer on Windows

• Start Designer, create a form
• Drag a widget from the widget box onto the form
• Note the Forbidden Cursor

Note:

• Introduced by f6bf4b2baa91e55f40596bf3f2823b119fdfa5e0
• The same happens for dragging actions from the action editor to a menu/toolbar.
• Both cases use QMimeData-derived classes.
• tools/designer/src/components/formeditor/tool_widgeteditor.cpp:WidgetEditorTool::handleDragEnterMoveEvent is never called.