Use skvm infix in gradients

Change-Id: Iff3bee6b94a6a196617960554b158720cde97c32
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/281156
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Reed <reed@google.com>
4 files changed