[graphite] Strict subsetting by default in image shader

For now only clamp and mirror tile modes are fully working; repeat needs
additional work with linear filtering and decal is still not
implemented.

Bug: b/238754369
Change-Id: I52c841f0edb4fd6a753c61fc7e832e76e8826035
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/580202
Commit-Queue: James Godfrey-Kittle <jamesgk@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
2 files changed