Add SkRasterPipeline blitter.

This is now pixel-exact with the existing sRGB SW impl as far as I've tested.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2146413002
CQ_INCLUDE_TRYBOTS=master.client.skia:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD-Trybot

Review-Url: https://codereview.chromium.org/2146413002
10 files changed