Views do not scroll when moving header sections outside the viewport

If the QHeaderView(s) of a view (QTableView etc.) is movable, the views do not scroll when the user is about to move a header section outside the viewport. This makes it hard to move a header section in general, and may make it impossible to move a header section where the user wants it.

Views should scroll appropriately when the user is about to move a header section outside the view's viewport.