[Gen C\C++ API docs] Fix documentation warnings for new autoEP/compile APIs (#24661)
### Description
Fixes documentation errors in comments within onnxruntime_c_api.h and
onnxruntime__cxx_api.h.
### Motivation and Context
The [Generate C/C++ API
docs](https://github.com/microsoft/onnxruntime/actions/runs/14855108283/job/41706460753#logs)
action is failing with error:
```shell
Run mkdir -p build/doxygen
/mnt/vss/_work/onnxruntime/onnxruntime/include/onnxruntime/core/session/onnxruntime_cxx_api.h:775: error: explicit link request to 'OrtKeyValuePair' could not be resolved (warning treated as error, aborting now)
```