polytf

This reinstates a simpler transfer function form, this time

   Cx                     x < D
   Ax^3 + Bx^2 + (1-A-B)  x ≥ D

Which is the form we use today for from_srgb() in Skia.

Change-Id: I97f57e336a8595fb7d2280088b636cdc4dbaa508
Reviewed-on: https://skia-review.googlesource.com/123500
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
26 files changed