[graphite] Move blendInfo from gatherer to builder

We have a SkPaintParamsKeyBuilder at precompile time but not a
SkPipelineDataGatherer. We need the blend info at precompilation
time so that we can create a complete SkShaderCodeDictionary entry
for the precompiled combination(s).

Bug: skia:12701
Change-Id: I7686162ba93cb331f7c7dc2422e2d6937f367397
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/547820
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
6 files changed