SkNx: use SK_ALWAYS_INLINE thoroughly.

SkNx: use SK_ALWAYS_INLINE thoroughly.

MSVC's not so good at inlining.  So tell it where to.  It won't hurt the others.

This has nothing directly to do with ODR safety.  The anonymous namespaces and 'static' on freestanding functions provide the correctness we need there.  But this change can help to mechanically prevent the sort of problems ODR violations can lead to.

I may follow up by extending this strategy further to Sk4px, which is used to implement a lot of the legacy xfermodes.

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=3608
CQ_INCLUDE_TRYBOTS=master.client.skia:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD-Trybot

Change-Id: I927334c40910ce43da1fbabdf243c9cd5438bea6
Reviewed-on: https://skia-review.googlesource.com/3608
Reviewed-by: Matt Sarett <msarett@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>