BoxCollider2D box = gameObject.AddComponent<BoxCollider2D>();
box.size = new Vector2(1.0f, 1.0f);//默认size很小，需要初始化否则检测不到东西
unity2018版本默认加载的package可以通过更新路径D:\Program Files\Unity\Editor\Data\Resources\PackageManager\Editor\manifest.json 里面字段defaultDependencies：
里面新包移除
"com.unity.analytics": "3.2.2",
"com.unity.purchasing": "2.0.3",
"com.unity.ads": "2.3.1",
"com.unity.textmeshpro": "1.3.0",
"com.unity.package-manager-ui": "2.0.3",
"com.unity.collab-proxy": "1.2.15",
