Miscellaneous color space refactors

(1) Use float matrix[16] everywhere (enables future code
    sharing).
(2) SkColorLookUpTable refactors
    *** Store in a single allocation (like SkGammas)
    *** Eliminate fOutputChannels (we always require 3,
        and probably always will)
(3) Change names of read_big_endian_* helpers

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2166093003
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/2166093003
6 files changed