Expose cxx standard (onnx#6625)

### Description
- Expose cxx standard

### Motivation and Context

CXX standard exposure is required to properly build against ONNX
library.

Example of the issue
microsoft/vcpkg#42942 (comment)

Generated target will have new property:

![{33169E2C-86D0-4E3A-BFF6-E27E436043BC}](https://github.com/user-attachments/assets/0fffaf33-dcb6-4f7b-b402-7605ddc7e73a)

Signed-off-by: Ilya Lavrenov <ilya.lavrenov@intel.com>
Signed-off-by: seungwoo-ji <seungwoo.ji@nuvilab.com>

CMakeLists.txt

@@ -492,6 +492,7 @@ else()
   set_target_properties(onnx_proto PROPERTIES VISIBILITY_INLINES_HIDDEN 1)
 endif()
 target_compile_definitions(onnx_proto PRIVATE ${ONNX_API_DEFINE})
+target_compile_features(onnx_proto PUBLIC cxx_std_${CMAKE_CXX_STANDARD})
 
 if(ONNX_USE_LITE_PROTO)
   if(TARGET protobuf::libprotobuf-lite)