It seems that MSVC + __vectorcall don't play well together,
so back ourselves out into a situation where we don't need it.
- Inline transfermode functions. This removes the need for SK_VECTORCALL.
- Remove 565 destination specializations.
Blending into 565 is not speed-critical enough to merit the code bloat.
- Removing 565 specializations means a bunch of Sk4px code is now dead.
8888 xfermodes generally speed up a bit from inlining, smoothly ranging from no change down to 0.65x for the fastest functions like Plus or Modulate.
565 xfermodes generally slow down because we're doing 565 -> 8888 and 8888->565 conversion serially[1] and using the stack, smoothly ranging from no change up to 2x slower for the fastest functions like Plus and Modulate.
[1] the 565->8888 conversion is actually being autovectorized
BUG=skia:4765,skia:4776
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1565223002
CQ_EXTRA_TRYBOTS=client.skia:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD-Trybot
No public API changes.
TBR=reed@google.com
Review URL: https://codereview.chromium.org/1565223002
defa0daa6a