feat: Add support for tool calling in ChatGoogleGenerativeAI

[davidmigloz]

Resolves #408

const tool = ToolSpec(
  name: 'get_current_weather',
  description: 'Get the current weather in a given location',
  inputJsonSchema: {
    'type': 'object',
    'properties': {
      'location': {
        'type': 'string',
        'description': 'The city and state, e.g. San Francisco, CA',
      },
    },
    'required': ['location'],
  },
);
final chatModel = ChatGoogleGenerativeAI(
  defaultOptions: ChatGoogleGenerativeAIOptions(
    model: 'gemini-1.5-pro-latest',
    temperature: 0,
    tools: [tool],
  ),
);
final res = await model.invoke(
  PromptValue.string('What’s the weather like in Boston and Madrid right now in celsius?'),
);

Check the docs for more information on how to use tools.