[VitisAI] fix graph save (#21293)

### Description
<!-- Describe your changes. -->
Revert the wrong change in
#20920


### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->
It would save the data at a wrong position

onnxruntime/core/providers/vitisai/imp/global_api.cc

@@ -126,7 +126,7 @@ static std::string config_to_json_str(const onnxruntime::ProviderOptions& config
 
 vaip_core::DllSafe<std::vector<std::unique_ptr<vaip_core::ExecutionProvider>>> compile_onnx_model(
     const onnxruntime::GraphViewer& graph_viewer, const logging::Logger& logger, const ProviderOptions& options) {
-  auto model_path = PathToUTF8String(ToPathString(graph_viewer.ModelPath().string()));
+  auto model_path = graph_viewer.ModelPath().string();
   if (s_library_vitisaiep.compile_onnx_model_with_options) {
     return vaip_core::DllSafe(s_library_vitisaiep.compile_onnx_model_with_options(model_path, graph_viewer.GetGraph(), options));
   } else {
@@ -227,9 +227,9 @@ vaip_core::OrtApiForVaip* create_org_api_hook() {
     auto& logger = logging::LoggingManager::DefaultLogger();
     auto& model = const_cast<onnxruntime::Model&>(const_model);
     auto model_proto = model.ToProto();
-    auto file_path = ToPathString(model.MainGraph().ModelPath().string());
+    auto file_path = model.MainGraph().ModelPath();
     auto local_registries = IOnnxRuntimeOpSchemaRegistryList{model.MainGraph().GetSchemaRegistry()};
-    auto ret = Model::Create(std::move(*model_proto), file_path, &local_registries, logger);
+    auto ret = Model::Create(std::move(*model_proto), ToPathString(file_path), &local_registries, logger);
     auto status = ret->MainGraph().Resolve();
     vai_assert(status.IsOK(), status.ErrorMessage());
     return ret.release();

onnxruntime/core/providers/vitisai/imp/graph.cc

@@ -107,12 +107,11 @@ void graph_save(const Graph& graph, const std::string& filename, const std::stri
   auto graph_proto_subgraph = graph.ToGraphProto();
   *model_proto->mutable_graph() = *graph_proto_subgraph;
   auto& logger = logging::LoggingManager::DefaultLogger();
-  auto filename_data_relative_path = std::filesystem::path();
   auto model = Model::Create(std::move(*model_proto), ToPathString(filename), nullptr, logger);
   if (initializer_size_threshold == std::numeric_limits<size_t>::max()) {
     model_proto = model->ToProto();
   } else {
-    model_proto = model->ToGraphProtoWithExternalInitializers(filename_dat, graph.ModelPath(), initializer_size_threshold);
+    model_proto = model->ToGraphProtoWithExternalInitializers(ToPathString(filename_dat), ToPathString(filename), initializer_size_threshold);
   }
   auto& metadata = model->MetaData();
   if (!metadata.empty()) {
@@ -124,7 +123,7 @@ void graph_save(const Graph& graph, const std::string& filename, const std::stri
       *prop->mutable_value() = m.second;
     }
   }
-  std::fstream output(filename, std::ios::out | std::ios::trunc | std::ios::binary);
+  std::fstream output(ToPathString(filename), std::ios::out | std::ios::trunc | std::ios::binary);
   bool result = model_proto->SerializeToOstream(output);
   output << std::flush;
   vai_assert(result, "model serialize to ostream error");