fix: Prevent changing DragEffects in TreeDataGrid DragDrop event-handlers if AutoDragDropRows=false

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• AutoDragDropRows check moved to the beginning of DragDrop event-handlers, before they perform any actions. This is necessary for inherited from TreeDataGrid types, with custom DragDrop event-handlers. Now e.DragDropEffects of DragOver event-handler is always None in inherited types, if AutoDragDropRows=false.

• Also AutoDragDropRows check moved to the beginning of RaiseRowDragStarted method, to prevent RowDragStartedEvent.

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