Merge "add Min to SkNi, specialized for u8 and u16 on SSE and NEON" into master-skia

https://skia.googlesource.com/skia/+/27e517ae533775889c98c65fa2f07b98357ecbc2

Change-Id: I9aee187f5a704b400beadfef4c062ab6601cd637