Add Meta and Structured Content to tool response

[zacksmash]

A few new fluent methods have been added to the text() response type for meta() and structuredContent(). You may use the methods as a getter or setter for the corresponding property.

These properties are then read in the CallTool method and returned in the response, if they're available.

Example:

#[IsReadOnly()]
class WeatherTool extends Tool
{
    // ...

    /**
     * Handle the tool request.
     */
    public function handle(Request $request, WeatherData $weatherData): Response
    {
        $city = $request->get('city');

        return Response::text("Here is the current weather information you requested for {$city}.")
            ->meta(['route' => 'weather'])
            ->structuredContent($weatherData->handle());
    }

Ref #99