Allow QWidget to have multiple cursors

At present a QWidget can have a single cursor, which applies to the whole widget. It would be useful to be able to assign several cursors to a widget, each associated with a smaller area.

At present 1-pixel splitter widgets can adjust their contentsMargins in order to be grabbable outside their drawn area. This makes them easier for people to grab if they're slightly off, however they can only show the resize cursor when the mouse is exactly over their drawn area.

Ideally the splitter would also be able to assign an extra cursor rectangle to its child widgets, to override their default cursor in this area with the appropriate resize cursor.

You can see this behaviour in iTunes; both the grab area and the resize cursor extend a few pixels either side of the single-pixel splitter line, which makes it easier to grab and easier to know when it's possible to grab.