pointer handlers need both gesture-duration and accumulated properties with setters

This is a generalization of QTBUG-68941, to which we responded by making PinchHandler.scale be the accumulated scale (for easy binding to Item.scale), while activeScale is the value that resets to 1 each time a gesture begins. We should have followed through and done that with all such properties:

• PinchHandler.rotation
• PinchHandler.translation
• DragHandler.translation

WheelHandler.rotation is already that way. There's no activeRotation because many wheel events don't have phase: with an old-fashioned wheel mouse, we can't tell when the gesture begins and ends, so I guess activeRotation would tend to stay small (just the value from the previous or current event). But WheelHandler.rotation has a setter, and QTBUG-76379 is asking for PinchHandler.scale to have a way to reset the value.

So we can generalize that too: each of these properties should have setters. If the UI provides more than one way to translate an item, and if you are using a handler's translation property in a binding, you need to be able to set that property when the item is moved by alternate means. Likewise with rotation.