Move SkScalerContextEffects to SkScalerContext.h

Change-Id: Ibcbcc93d310e115bf5d8c683ac493100e3030988
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/244304
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Herb Derby <herb@google.com>
2 files changed