QS8 version of NHWC Convolution operator

- Operator implementation
- Unit tests
- Microbenchmarks

PiperOrigin-RevId: 324916339
diff --git a/src/operator-strings.c b/src/operator-strings.c
index 1e1dc38..f64316b 100644
--- a/src/operator-strings.c
+++ b/src/operator-strings.c
@@ -48,6 +48,8 @@
       return "Convolution (NHWC, F16)";
     case xnn_operator_type_convolution_nhwc_f32:
       return "Convolution (NHWC, F32)";
+    case xnn_operator_type_convolution_nhwc_qs8:
+      return "Convolution (NHWC, QS8)";
     case xnn_operator_type_convolution_nhwc_qu8:
       return "Convolution (NHWC, QU8)";
     case xnn_operator_type_convolution_nchw_f32: