[skif] Update DisplacementMap to use FilterResult and runtime sksl

Change-Id: Ie97fb3229de84f9951b9686ccfa8b4f768e7b0ca
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/701419
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
6 files changed