Starting to hack up HDR transfer function support

Brings over skcms' encoding scheme, etc.

Change-Id: Ib8abec911acd1c50df3b201b4a9bde01b1cb123b
Bug: chromium:960620
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/249000
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
diff --git a/RELEASE_NOTES.txt b/RELEASE_NOTES.txt
index 3bb9b0e..9223c43 100644
--- a/RELEASE_NOTES.txt
+++ b/RELEASE_NOTES.txt
@@ -10,6 +10,8 @@
 Milestone 79
 
 [Insert new notes here.]
+  * Added support for PQ and HLG transfer functions to SkColorSpace.
+
   * Added new api on GrContext ComputeImageSize. This replaces the hold static helper
     ComputeTextureSize.