[GPT-OSS] Structure_Tag support for gpt-oss tool-call in cot (#25515)

Signed-off-by: Hanchenli <lihanc2002@gmail.com>
Signed-off-by: Hanchenli <61769611+Hanchenli@users.noreply.github.com>
Signed-off-by: Wei Wei <wwei6@meta.com>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
Co-authored-by: Wei Wei <wwei6@meta.com>
Co-authored-by: Wei Wei <weiweinpu@gmail.com>
Co-authored-by: Cyrus Leung <tlleungac@connect.ust.hk>