Clean up GrSimpleTextureEffect.

Make it look human written instead of machine generated.

Use perspective texturing builtin sample() when coords are three component
rather than dividing to make them 2d.

Change-Id: I9694857beaf35733077d0472d1eae43b5da933d0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/261677
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
2 files changed