[CXX] Introduce C++ API for new C entry points (microsoft#25897)

### Description
<!-- Describe your changes. -->
Create or augment existing C++ API for new entry points

### 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. -->
Enable exception safe coding in C++ codebase.

Author: yuslepukhin

include/onnxruntime/core/providers/utils/ort_graph_to_proto.h

@@ -54,7 +54,7 @@ class ExampleEp : public OrtEp, public ApiPtrs {
   OrtStatus* CreateEpContextNodes(gsl::span<const OrtNode*> fused_nodes,
                                   /*out*/ gsl::span<OrtNode*> ep_context_nodes);
 
-  OrtStatus* ExampleEp::SaveConstantInitializers(const OrtGraph* graph);
+  OrtStatus* SaveConstantInitializers(const OrtGraph* graph);
 
   ExampleEpFactory& factory_;
   std::string name_;

include/onnxruntime/core/session/onnxruntime_cxx_api.h

@@ -1,6 +1,10 @@
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT License.
 
+#define ORT_API_MANUAL_INIT
+#include "onnxruntime_cxx_api.h"
+#undef ORT_API_MANUAL_INIT
+
 #include "ep_factory.h"
 
 // To make symbols visible on macOS/iOS
@@ -21,6 +25,9 @@ EXPORT_SYMBOL OrtStatus* CreateEpFactories(const char* registration_name, const
   const OrtEpApi* ep_api = ort_api->GetEpApi();
   const OrtModelEditorApi* model_editor_api = ort_api->GetModelEditorApi();
 
+  // Manual init for the C++ API
+  Ort::InitApi(ort_api);
+
   // Factory could use registration_name or define its own EP name.
   std::unique_ptr<OrtEpFactory> factory = std::make_unique<ExampleEpFactory>(registration_name,
                                                                              ApiPtrs{*ort_api, *ep_api,

include/onnxruntime/core/session/onnxruntime_cxx_inline.h

@@ -5,48 +5,33 @@
 
 #include <string>
 
-OrtStatus* GetSessionConfigEntryOrDefault(const OrtApi& ort_api, const OrtSessionOptions& session_options,
+OrtStatus* GetSessionConfigEntryOrDefault(const OrtApi& /* ort_api */, const OrtSessionOptions& session_options,
                                           const char* config_key, const std::string& default_val,
                                           /*out*/ std::string& config_val) {
-  int has_config = 0;
-  RETURN_IF_ERROR(ort_api.HasSessionConfigEntry(&session_options, config_key, &has_config));
-
-  if (has_config != 1) {
-    config_val = default_val;
-    return nullptr;
+  try {
+    Ort::ConstSessionOptions sess_opt{&session_options};
+    config_val = sess_opt.GetConfigEntryOrDefault(config_key, default_val);
+  } catch (const Ort::Exception& ex) {
+    Ort::Status status(ex);
+    return status.release();
   }
 
-  size_t size = 0;
-  RETURN_IF_ERROR(ort_api.GetSessionConfigEntry(&session_options, config_key, nullptr, &size));
-
-  config_val.resize(size);
-  RETURN_IF_ERROR(ort_api.GetSessionConfigEntry(&session_options, config_key, config_val.data(), &size));
-  config_val.resize(size - 1);  // remove the terminating '\0'
-
   return nullptr;
 }
 
-OrtStatus* IsFloatTensor(const OrtApi& ort_api, const OrtValueInfo* value_info, bool& result) {
+void IsFloatTensor(Ort::ConstValueInfo value_info, bool& result) {
   result = false;
 
-  const OrtTypeInfo* type_info = nullptr;
-  RETURN_IF_ERROR(ort_api.GetValueInfoTypeInfo(value_info, &type_info));
-
-  ONNXType onnx_type = ONNX_TYPE_UNKNOWN;
-  RETURN_IF_ERROR(ort_api.GetOnnxTypeFromTypeInfo(type_info, &onnx_type));
+  auto type_info = value_info.TypeInfo();
+  ONNXType onnx_type = type_info.GetONNXType();
   if (onnx_type != ONNX_TYPE_TENSOR) {
-    return nullptr;
+    return;
   }
 
-  const OrtTensorTypeAndShapeInfo* type_shape = nullptr;
-  RETURN_IF_ERROR(ort_api.CastTypeInfoToTensorInfo(type_info, &type_shape));
-
-  ONNXTensorElementDataType elem_type = ONNX_TENSOR_ELEMENT_DATA_TYPE_UNDEFINED;
-  RETURN_IF_ERROR(ort_api.GetTensorElementType(type_shape, &elem_type));
+  auto type_shape = type_info.GetTensorTypeAndShapeInfo();
+  ONNXTensorElementDataType elem_type = type_shape.GetElementType();
   if (elem_type != ONNX_TENSOR_ELEMENT_DATA_TYPE_FLOAT) {
-    return nullptr;
+    return;
   }
-
   result = true;
-  return nullptr;
 }

onnxruntime/test/autoep/library/ep.cc

@@ -107,4 +107,4 @@ OrtStatus* GetSessionConfigEntryOrDefault(const OrtApi& ort_api, const OrtSessio
                                           /*out*/ std::string& config_val);
 
 // Returns true (via output parameter) if the given OrtValueInfo represents a float tensor.
-OrtStatus* IsFloatTensor(const OrtApi& ort_api, const OrtValueInfo* value_info, bool& result);
+void IsFloatTensor(Ort::ConstValueInfo value_info, bool& result);