More shader preliminaries / refactoring

    - thread through ctm
    - make blitter handle paint modulation instead of each shader

TBR=herb@google.com

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4830
CQ_INCLUDE_TRYBOTS=master.client.skia:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD-Trybot

Change-Id: I8161e6b3864c4e48e4d47d5ad40a56a13c02fee8
Reviewed-on: https://skia-review.googlesource.com/4830
Reviewed-by: Mike Klein <mtklein@chromium.org>
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
9 files changed