Making handles setters based on field attributes

[BrunoSilvaFreire]

For example, adding a PositionHandleAttribute to a field, would draw a position handle to scene for more intuitive editing of the property

    public class MyToken : IToken {
        public ExposedReference<ParticleSystem> System;
        [PositionHandle]
        public Vector3 Position;

        public IEnumerator Execute(CutscenePlayer player) {
            var systemInScene = System.Resolve(player);
            Object.Instantiate(systemInScene, Position, Quaternion.identity);
            yield break;
        }
    }