add back Sk4i

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1699293002

Review URL: https://codereview.chromium.org/1699293002
diff --git a/src/core/SkNx.h b/src/core/SkNx.h
index 986c133..8722bf6 100644
--- a/src/core/SkNx.h
+++ b/src/core/SkNx.h
@@ -199,6 +199,8 @@
 typedef SkNx<4,  uint16_t> Sk4h;
 typedef SkNx<16, uint16_t> Sk16h;
 
+typedef SkNx<4, int> Sk4i;
+
 // Include platform specific specializations if available.
 #if !defined(SKNX_NO_SIMD) && SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_SSE2
     #include "../opts/SkNx_sse.h"