Migrate openai tools to langchain tools without callable

[rong-xyz]

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Example Code

tools = [{
    "type": "function",
    "function": {
        "name": "write_paragraph",
        "description": "Write a paragraph about a given topic.",
        "parameters": {
            "type": "object",
            "properties": {
                "paragraph": {
                    "type": "string",
                    "description": "The paragraph to write."
                }
            },
            "required": [
                "paragraph"
            ],
        },
    }
}]

Description

We having being self maintaining llm calls from multiple provider and now would like to use langchain to solve this issue. However, I found that langchain forced us to provide a callable func to create tools:langchain_core.tools.Tool, which is not required by any of the foundation model providers. Assuming that we want to replicate the exact behavior of a llm call with the same system prompt, messages and tools

System Info

irrelevant