Make all SkRasterPipeline stages stock stages in SkOpts.

If we want to support VEX-encoded instructions (AVX, F16C, etc.) without a ridiculous slowdown, we need to make sure we're running either all VEX-encoded instructions or all non-VEX-encoded instructions.  That means we cannot mix arbitrary user-defined SkRasterPipeline::Fn (never VEX) with those living in SkOpts (maybe VEX)... it's SkOpts or bust.

This ports the existing user-defined SkRasterPipeline::Fn use cases over to use stock stages from SkOpts.  I rewrote the unit test to use stock stages, and moved the SkXfermode implementations to SkOpts.  The code deleted for SkArithmeticMode_scalar should already be dead.


BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2940
CQ_INCLUDE_TRYBOTS=master.client.skia:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD-Trybot

Change-Id: I94dbe766b2d65bfec6e544d260f71d721f0f5cb0
Reviewed-on: https://skia-review.googlesource.com/2940
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Mike Reed <reed@google.com>
7 files changed