Fix tile modes in SkGpuBlurUtils.

Expand direct GM testing of SkGpuBlurUtils.

Decimate in SkGpuBlurUtils using GrSurfaceContext::rescale.
GrSurfaceContext::rescale() works on recording context and
uses approximate textures (to avoid memory issues for blurs
of many different sizes).

Don't preserve contents to the top/left of the source bounds
in the rescaled image.

GrGaussianConvolutionFragmentProcessor applies wrap mode to
both axes.

Rely on GrTextureEffect to omit subset enforcement in shader
by providing a domain rect rather than turning off tiling in
caller.

Change-Id: I73e09b4fcbcbed590dd3599091c38d5de65f48c4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/285099
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
12 files changed