Adding a constant node type

In order to create a constant node of a certain type, a node view for that particular type needs to be defined.

Here's an example of a constant node view for an enum:

using System;
using InsaneScatterbrain.ScriptGraph;
using InsaneScatterbrain.ScriptGraph.Editor;
using UnityEditor.UIElements;

// Adding this attribute adds the node view to the graph's context menu under "Constant"
[ConstantNodeView(typeof(MyEnum))]
public class MyEnumConstantNodeView : ConstantNodeView
{
    public MyEnumConstantNodeView(ConstantNode node, ScriptGraphView graphView) : base(node, graphView)
    {
        var myEnumValue = (MyEnum) node.Value;
        // AddDefaultField creates the EnumField and makes sure that value changes are persisted.
        var field = AddDefaultField<Enum, EnumField>(myEnumValue);  
    
        // Init needs to be called to make the field aware of the enum's specific type.
        // The field will be empty otherwise.
        field.Init(myEnumValue);    
    }
}