Create Legacy AnimationClips using the Asset Menu in Unity

CreateLegacyAnimationClip.cs

using System.IO;
using UnityEditor;
using UnityEngine;

public class CreateLegacyAnimationClip {

	[MenuItem("Assets/Create/Animation (Legacy)", false, 402)]
	public static void CreateIt()
	{
		AnimationClip clip = new AnimationClip();
		clip.legacy = true;
		
		// via https://forum.unity.com/threads/how-to-get-currently-selected-folder-for-putting-new-asset-into.81359/
		string path = "Assets";
		foreach (UnityEngine.Object obj in Selection.GetFiltered(typeof(UnityEngine.Object), SelectionMode.Assets))
		{
			path = AssetDatabase.GetAssetPath(obj);
			if (File.Exists(path))
			{
				path = Path.GetDirectoryName(path);
			}
			break;
		}

		AssetDatabase.CreateAsset(clip, path+"/New Legacy Animation.anim");
	}
}