[graphite] Cubic filtering in image shader

If we decide we don't want to pass in a 4x4 matrix uniform every time we
use an image shader, we can perhaps a) pass in the B and C parameters
instead, or b) use a separate shader snippet for cubic filtering.

Bug: b/238754369
Change-Id: I6747db74321f12b6ccc78b138456f16e5d6a2767
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/585836
Commit-Queue: James Godfrey-Kittle <jamesgk@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
4 files changed