Add SkSpecialImage::extractSubset & NewFromPixmap

This is calved off of: https://codereview.chromium.org/1785643003/ (Switch SkBlurImageFilter over to new onFilterImage interface)

This now relies on: https://codereview.chromium.org/1813483002/ (ImagePixelLocker now manually allocates SkPixmap) to clean up the uses of SkAutoPixmapStorage in Chromium

GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1787883002

Committed: https://skia.googlesource.com/skia/+/250581493a0859987e482810879e85e5ac2dc002

Review URL: https://codereview.chromium.org/1787883002
19 files changed