Plumb lighting props and implement a Phong lighting model.
This is ~40% slower with the SW backend - to mitigate, construct two
runtime effects and only apply fancy lighting when needed.
Change-Id: If6f71253e7adc148f6d5cf5fbde2c1dff977f669
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/368246
Commit-Queue: Florin Malita <fmalita@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
