[Platform] Support built-in and MCP tool calling for OpenAI #825
Description
The Responses API supports many more tools than the Chat Completions API.
What we currently support is only function tool calls, as that was the only sort of tool call supported by Chat Completions. When #796 is closed, we should add support for these built-in and MCP tools.
This is something I ran into while migrating to the Responses API, but decided it's OOS for #796.