Fix the issue that the new generated EP context model not able to fin…

…d external data (#23537)

Fix the issue that the new generated EP context model not able to find external data

### Description
The new generated EP context model was not able to find the external data file because it lost track of the source model path which used to locate the external initializers.

Relate to issue: #23358

onnxruntime/core/framework/graph_partitioner.cc

@@ -683,7 +683,9 @@ static Status CreateEpContextModel(const ExecutionProviders& execution_providers
                            context_cache_path, "' exist already.");
   }
 
-  Model ep_context_model(graph.Name(), false, graph.GetModel().MetaData(), PathString(), IOnnxRuntimeOpSchemaRegistryList{graph.GetSchemaRegistry()},
+  Model ep_context_model(graph.Name(), false, graph.GetModel().MetaData(),
+                         graph.GetModel().ModelPath(),  // use source model path so that external initializers can find the data file path
+                         IOnnxRuntimeOpSchemaRegistryList{graph.GetSchemaRegistry()},
                          graph.DomainToVersionMap(), {}, logger);
   auto& ep_graph = ep_context_model.MainGraph();
   ep_graph.SetDescription(graph.Description());

onnxruntime/test/providers/qnn/qnn_ep_context_test.cc

@@ -202,13 +202,15 @@ void EpCtxCpuNodeWithExternalIniFileTestBody(bool expect_external_ini_file) {
   helper.SetGraphOutputs();
   ASSERT_STATUS_OK(model.MainGraph().Resolve());
   ModelSavingOptions model_saving_options{10};
-  const std::string model_with_ext = "model_external.onnx";
+  // dump the model in testdata folder in case it hides the bug that not able to find model not in current dir
+  const std::string model_with_ext = "./testdata/model_external.onnx";
   const std::string model_ext_file = "model_external.bin";
   ASSERT_STATUS_OK(Model::SaveWithExternalInitializers(model, model_with_ext,
                                                        model_ext_file, model_saving_options));
 
   EXPECT_TRUE(std::filesystem::exists(model_with_ext.c_str()));
-  EXPECT_TRUE(std::filesystem::exists(model_ext_file.c_str()));
+  std::string model_ext_file_full_path = "./testdata/" + model_ext_file;
+  EXPECT_TRUE(std::filesystem::exists(model_ext_file_full_path.c_str()));
 
   Ort::SessionOptions so;
   so.AddConfigEntry(kOrtSessionOptionEpContextEnable, "1");
@@ -233,7 +235,7 @@ void EpCtxCpuNodeWithExternalIniFileTestBody(bool expect_external_ini_file) {
 
   // clean up
   ASSERT_EQ(std::remove(model_with_ext.c_str()), 0);
-  ASSERT_EQ(std::remove(model_ext_file.c_str()), 0);
+  ASSERT_EQ(std::remove(model_ext_file_full_path.c_str()), 0);
   ASSERT_EQ(std::remove(ep_context_model_file.c_str()), 0);
 }