[Feature Request] Support callback function as autoClose value

`autoClose` property for the Toast container is a number right now,
therefore I can't set a dynamic value to it depending on how long the text should be shown.

So basically, the property would change from

`autoClose?: number | false` to `autoClose?: ((message: ToastContent) => number | false) | number | false`

I want to receive at least the `ReactNode` of the toast message about to be shown and return the autoClose value in ms or false if neccessary.