Update DeviceSpaceEffect and ColorSpaceXform to return half4s.

This is slightly more efficient than assigning to sk_OutColor; it saves
one assignment in the optimized code.

Change-Id: I225c428a2b0bfdb0da4b60c6a8b488f104868ea7
Bug: skia:10549
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/336216
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
4 files changed