Add support for decomposition of iOS 9 multi-dimensional spring velocity.
Add support for decomposition of iOS 9 multi-dimensional spring velocity.

Summary:
Core Animation springs do not support multi-dimensional velocity. The only way to support multi-dimensional velocity is to decompose multi-dimensional springs into their component parts and add individual one-dimensional animations for each.

This diff adds support for additive CGPoint spring animation velocity.

Reviewers: O2 Material Motion, O4 Material Apple platform reviewers, #material_motion, chuga

Reviewed By: O4 Material Apple platform reviewers, chuga

Tags: #material_motion

Differential Revision: http://codereview.cc/D2633

material-motion/material-motion-swift,material-motion/material-motion-swift