Release Note: Trackpad scrolling of text on OS X 10.12 Sierra is very fast

The `MouseWheelEvent.getWheelRotation()` method returned rounded native `NSEvent deltaX/Y` events on Mac OS X.
The latest macOS Sierra 10.12 produces very small `NSEvent deltaX/Y` values so rounding and summing them leads to the huge value returned from the `MouseWheelEvent.getWheelRotation()`.
The JDK-8166591 fix accumulates `NSEvent deltaX/Y` and the `MouseWheelEvent.getWheelRotation()` method returns non-zero values only when the accumulated value exceeds a threshold and zero value.
This is compliant with the `MouseWheelEvent.getWheelRotation()` specification:

<https://docs.oracle.com/javase/8/docs/api/java/awt/event/MouseWheelEvent.html#getWheelRotation-->

>Returns the number of "clicks" the mouse wheel was rotated, as an integer. A partial rotation may occur if the mouse supports a high-resolution wheel. In this case, the method returns zero until a full "click" has been accumulated.

For the precise wheel rotation values, use the `MouseWheelEvent.getPreciseWheelRotation()` method instead.