Expose UserState and the node id to value_widget

[setzer22]

This changes the signature for value_widget to provide additional information:

    fn value_widget(
        &mut self,
        param_name: &str,
        node_id: NodeId, // NEW
        ui: &mut egui::Ui,
        user_state: &mut Self::UserState, // NEW
    ) -> Vec<Self::Response>;

This allows more flexible implementations for inline widgets, where the behavior of the widget depends not only on the ValueType but additional data that might be stored in the UserState.

[setzer22]

Also exposed UserState to the three methods in NodeTemplateTrait. This is useful for when the NodeTemplate struct does not contain the data, but some key to that data. Users can then store the actual table inside UserState and query it when needed.

[setzer22]

Finally, this also adds the NodeData parameter when drawing the value widget. This required an extra Default trait bound, which hopefully shouldn't cause too much trouble on user crates. An unsafe solution exists that didn't require the trait bound, but I don't consider it worth it.