Fix GrTextureEffect with kRepeat/kRepeat/kBilerp.

Use absolute error value when doing shader-based interp between all
four subset corner texels.

Add 2x2 image to rectangle_texture GM and draw with all combos of
tile modes.

Change-Id: Ia5856d592b1c9ab8b588301e7b659b05a7439396
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/272920
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
2 files changed