[WebNN EP] Update Op Softmax for readability

Improve readability by fixing misplaced comments and utilizing std::rotate.

onnxruntime/core/providers/webnn/builders/impl/softmax_op_builder.cc

@@ -69,8 +69,7 @@ Status SoftmaxOpBuilder::AddToModelBuilderImpl(ModelBuilder& model_builder,
       emscripten::val options = emscripten::val::object();
       std::vector<uint32_t> permutation(input_shape.size());
       std::iota(permutation.begin(), permutation.end(), 0);
-      permutation.erase(permutation.begin() + axis);
-      permutation.push_back(axis);
+      std::rotate(permutation.begin() + axis, permutation.begin() + axis + 1, permutation.end());
       options.set("permutation", emscripten::val::array(permutation));
       input = model_builder.GetBuilder().call<emscripten::val>("transpose", input, options);
     }
@@ -87,7 +86,7 @@ Status SoftmaxOpBuilder::AddToModelBuilderImpl(ModelBuilder& model_builder,
 
     output = model_builder.GetBuilder().call<emscripten::val>("softmax", input);
 
-    // Transpose back to the axis.
+    // Restore from 2-D to the original shape.
     if (input_shape.size() != 2) {
       std::vector<uint32_t> new_shape;
       std::transform(input_shape.begin(), input_shape.begin() + axis, std::back_inserter(new_shape),
@@ -98,13 +97,12 @@ Status SoftmaxOpBuilder::AddToModelBuilderImpl(ModelBuilder& model_builder,
       output = model_builder.GetBuilder().call<emscripten::val>("reshape",
                                                                 output, emscripten::val::array(new_shape));
     }
-    // Reshape to the original shape.
+    // Restore the corresponding axis back to the initial position from the last position.
     if (axis != static_cast<int>(input_shape.size() - 1)) {
       emscripten::val options = emscripten::val::object();
       std::vector<uint32_t> permutation(input_shape.size());
       std::iota(permutation.begin(), permutation.end(), 0);
-      permutation.pop_back();
-      permutation.insert(permutation.begin() + axis, input_shape.size() - 1);
+      std::rotate(permutation.rbegin(), permutation.rbegin() + 1, permutation.rend() - axis);
       options.set("permutation", emscripten::val::array(permutation));
       output = model_builder.GetBuilder().call<emscripten::val>("transpose", output, options);
     }