Support plugin EPs with original SessionOptionsAppendExecutionProvider API

[adrianlizarraga]

Description

Draft only. May not be merged.

Allows an application to use SessionOptionsAppendExecutionProvider with a plugin EP from a library registered with ORT. The SessionOptionsAppendExecutionProvider implementation first tries to use an EP built with ORT. If not found, it looks for a plugin EP with the matching name. If a plugin EP exists, an EP factory with all OrtEpDevice instances it supports is added to the session options.

 const OrtApi& c_api = Ort::GetApi();
  ASSERT_ORTSTATUS_OK(c_api.RegisterExecutionProviderLibrary(*ort_env,
                                                             Utils::example_ep_info.registration_name.c_str(),
                                                             Utils::example_ep_info.library_path.c_str()));
  const std::string& plugin_ep_name = Utils::example_ep_info.registration_name;

  {
    Ort::SessionOptions session_options;
    std::unordered_map<std::string, std::string> ep_options;
    session_options.AppendExecutionProvider(plugin_ep_name, ep_options);  // Support added by this PR

    Ort::ModelCompilationOptions compile_options(*ort_env, session_options);
    compile_options.SetFlags(OrtCompileApiFlags::OrtCompileApiFlags_ERROR_IF_NO_NODES_COMPILED);
    compile_options.SetInputModelPath(input_model_file);
    compile_options.SetOutputModelPath(output_model_file);

    Ort::Status status = Ort::CompileModel(*ort_env, compile_options);
  }

  ASSERT_ORTSTATUS_OK(c_api.UnregisterExecutionProviderLibrary(*ort_env,
                                                               Utils::example_ep_info.registration_name.c_str()));

Motivation and Context