Refactor X32 PAD micro-kernels

Unify interface for X32 PAD and X32 FILL

PiperOrigin-RevId: 312865535
diff --git a/BUILD.bazel b/BUILD.bazel
index f872073..6d49183 100644
--- a/BUILD.bazel
+++ b/BUILD.bazel
@@ -268,7 +268,8 @@
     "src/x32-packx/x2-scalar.c",
     "src/x32-packx/x3-scalar.c",
     "src/x32-packx/x4-scalar.c",
-    "src/x32-pad/x2-scalar.c",
+    "src/x32-pad/scalar-int.c",
+    "src/x32-pad/scalar-float.c",
     "src/x32-unpool/scalar.c",
     "src/x32-zip/x2-scalar.c",
     "src/x32-zip/x3-scalar.c",
@@ -483,7 +484,7 @@
     "src/f32-vmulcaddc/gen/c8-minmax-psimd-2x.c",
     "src/x32-fill/psimd.c",
     "src/x32-packx/x4-psimd.c",
-    "src/x32-pad/x2-psimd.c",
+    "src/x32-pad/psimd.c",
     "src/x32-unpool/psimd.c",
     "src/x32-zip/x2-psimd.c",
     "src/x32-zip/x3-psimd.c",
@@ -689,7 +690,7 @@
     "src/u8-rmax/neon.c",
     "src/x32-fill/neon.c",
     "src/x32-packx/x4-neon-st4.c",
-    "src/x32-pad/x2-neon.c",
+    "src/x32-pad/neon.c",
     "src/x32-unpool/neon.c",
     "src/x32-zip/x2-neon.c",
     "src/x32-zip/x3-neon.c",
@@ -1115,6 +1116,7 @@
     "src/f32-vmulcaddc/gen/c8-minmax-sse-2x.c",
     "src/x32-fill/sse.c",
     "src/x32-packx/x4-sse.c",
+    "src/x32-pad/sse.c",
     "src/math/roundne-sse-addsub.c",
     "src/math/roundd-sse-addsub.c",
     "src/math/roundu-sse-addsub.c",
@@ -1157,7 +1159,6 @@
     "src/u8-clamp/sse2-x64.c",
     "src/u8-maxpool/9p8x-minmax-sse2-c16.c",
     "src/u8-rmax/sse2.c",
-    "src/x32-pad/x2-sse2.c",
     "src/x32-unpool/sse2.c",
     "src/x32-zip/x2-sse2.c",
     "src/x32-zip/x3-sse2.c",