Switch SkBlurImageFilter over to new onFilterImage interface

This CL relies on:
https://codereview.chromium.org/1787883002/ (Add SkSpecialImage::extractSubset & NewFromPixmap)
https://codereview.chromium.org/1808743003/ (Allow SkGpuDevice::drawSprite to handle subset SkBitmaps)
https://codereview.chromium.org/1813813002/ (Add SkSpecialImage::makeTextureImage entry point)

GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1785643003

Review URL: https://codereview.chromium.org/1785643003
7 files changed