Add support for F32 sources to SkColorSpaceXform

This also subtlely allows clients to convert between F32 and F16.

BUG=skia:

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

Change-Id: Ied5f2295fce00c69d8cf85730be899f3f8597915
Reviewed-on: https://skia-review.googlesource.com/9914
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Matt Sarett <msarett@google.com>
6 files changed