Calls Animancer.AnimancerPlayable.GetKey(UnityEngine.AnimationClip) and returns the state which registered with that key or creates one if it doesn't exist.

If the state already exists but has the wrong Animancer.AnimancerState.Clip, the `allowSetClip` parameter determines what will happen. False causes it to throw an System.ArgumentException while true allows it to change the Animancer.AnimancerState.Clip. Note that the change is somewhat costly to performance so use with caution.

public AnimancerState GetOrCreate(AnimationClip clip, bool allowSetClip = false)