Disable dp4a matmul on macOS, since metal does not appear to have DP4…

…A in its instruction set.

onnxruntime/contrib_ops/webgpu/quantization/matmul_nbits.cc

@@ -782,9 +782,12 @@ Status MatMulNBits::ComputeInternal(onnxruntime::webgpu::ComputeContext& context
 
   const bool has_zero_points = zero_points != nullptr;
   const bool has_subgroup = context.Device().HasFeature(wgpu::FeatureName::Subgroups);
+  // macOS - Avoid using dp4a on Metal, as it does not appear to have native dp4a support.
+  // https://github.com/gpuweb/gpuweb/issues/2677#issuecomment-1713292226
+  const bool use_dp4a = has_subgroup && context.AdapterInfo().backendType != wgpu::BackendType::Metal;
   if (accuracy_level_ == 4 && block_size == 32 &&
       batch_count == 1 && components_a == 4 && K % 64 == 0 && N % 16 == 0 &&
-      !has_zero_points && has_subgroup && M >= kMinMForTileOptimization) {
+      !has_zero_points && use_dp4a && M >= kMinMForTileOptimization) {
     constexpr uint32_t kVec4Components = 4;
     constexpr uint32_t kVec2Components = 2;
     constexpr uint32_t kU32Components = 4;