vertexai[patch]: ChatVertexAI.generate, stream, bind_tools

[baskaryan]

• Update bind_tools to construct a dict that matches VertexAI Tool proto and bind that to the model
• Update bind_tools to accept FunctionDeclaration and Vertex Tool directly
• Update bind_tools to accept a tool_choice param for easier tool_config setting
• Refactor generate, agenerate, stream, astream to reuse gemini param setting and response parsing

[efriis]

big fan of the gemini/non gemini split

[baskaryan]

note: tests/integration_tests/test_chat_models.py::test_chat_vertexai_gemini_function_calling_with_multiple_parts fails non-deterministically

[lkuligin]

nits: should we add to the docstring an example how to contsruct _ToolConfigDict and _ToolChoiceType?

so that people don't need to read the source code.

[alx13]

+1 for splitting gemini vs non-gemini.

WDYT if we make this method to only select which function to run, and move gemini implementation to _generate_gemini (and obviously in other methods) like this:

    def _generate(
        self,
        messages: List[BaseMessage],
        stop: Optional[List[str]] = None,
        run_manager: Optional[CallbackManagerForLLMRun] = None,
        stream: Optional[bool] = None,
        **kwargs: Any,
    ) -> ChatResult:
        if stream is True or (stream is None and self.streaming):
            stream_iter = self._stream(
                messages, stop=stop, run_manager=run_manager, **kwargs
            )
            return generate_from_stream(stream_iter)
        if not self._is_gemini_model:
            return self._generate_non_gemini(messages, stop=stop, **kwargs)
        return self._generate_gemini(messages, stop=stop, **kwargs)


    def _generate_gemini(
        self,
        messages: List[BaseMessage],
        stop: Optional[List[str]] = None,
        **kwargs: Any,
    ):
        client, contents = self._gemini_client_and_contents(messages)
        params = self._gemini_params(stop=stop, **kwargs)
        with telemetry.tool_context_manager(self._user_agent):
            response = client.generate_content(contents, **params)
        return self._gemini_response_to_chat_result(response)

    def _generate_non_gemini(
        self,
        messages: List[BaseMessage],
        stop: Optional[List[str]] = None,
        **kwargs: Any,
    ) -> ChatResult:
         ...

That would make testing a little bit cleaner.