Use texture for shadow falloff

Bug: b/142333639
Change-Id: I5c5bf4da0e2bb5f1b4233681dee305cf381c3e2a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/250096
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
3 files changed