Make raster pipeline support all pixel conversions

BUG=skia:

CQ_INCLUDE_TRYBOTS=skia.primary:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD

Change-Id: Idc76999d0f5591a567b3976cb9db829c350e4be2
Reviewed-on: https://skia-review.googlesource.com/8304
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Matt Sarett <msarett@google.com>
9 files changed