Adding Scale and Rotation pivots for Node

[Nir Lisker]

Hi,

I would like to implement properties for Node that control the pivots for
its built-in rotation and scaling transformations. Currently, it is
possible to do so only via a Rotate or Scale transforms, which are added to
the node's getTransforms list as both pivots are set to the Node's center.

This will make it easier to work with the built-in transforms and also
allow the scale and rotate transitions to bind to these new properties as
the next step, significantly reducing the complexity for these operations.
JBS issues have been filed in the past for this in [1] and its linked
issues.

The internal implementation changes will be in
Node#updateLocalToParentTransform() in the `if` block at line 5057 and will
include translation operations to and from the pivots. It's also possible
to separate the check for applying rotation and scaling to save on unneeded
operations, I believe.

One thing to look at carefully is the way the public API is defined. The
pivots can be represented by a Point3D or a double for each axis. Scale
transform use 3 doubles for both the scale amount and the pivot. Rotate
transform uses 3 doubles for the pivot and a Point3D for the axis. It's not
clear to me why this is the case.

As a side note, the scale and rotation built-in transforms are defined
internally in a specific order, and this order does not appear to be
documented. That is, if I setRotate(90) and setScaleX(2) I can not know
a-priori if I will scale X (scale before rotate) or Y (scale after rotate).

Comments are welcome.

- Nir

[1] https://bugs.openjdk.java.net/browse/JDK-8092304