[Unity][JSONUnity]JsonUtility出现错误

新建项目工程，这个manifest.json为空。

当在项目工程的脚本中使用JsonUtility，manifest.json文件会自动运行，

打开工程项目所在文件夹E:\Unity\UnityProjects\New Unity Project\Packages\manifest.json

如果显示JsonUtility出现错误，无法引用。

Assets/Scripts/JsonHelper.cs(9,30): error CS1070: The type `UnityEngine.JsonUtility' has been forwarded to an assembly that is not referenced. Enable the built in package 'JSONSerialize' in the Package Manager window to fix this error.
Assets/Scripts/JsonHelper.cs(9,42): error CS0023: The `.' operator cannot be applied to operand of type `UnityEngine.JsonUtility'
Assets/Scripts/JsonHelper.cs(17,28): error CS0023: The `.' operator cannot be applied to operand of type `UnityEngine.JsonUtility'
Assets/Scripts/JsonHelper.cs(24,28): error CS0023: The `.' operator cannot be applied to operand of type `UnityEngine.JsonUtility'

使得manifest.json包含以下内容

{
  "dependencies": {
    "com.unity.ads": "2.0.8",
    "com.unity.analytics": "2.0.16",
    "com.unity.package-manager-ui": "1.9.11",
    "com.unity.purchasing": "2.0.3",
    "com.unity.textmeshpro": "1.2.4",
    "com.unity.modules.ai": "1.0.0",
    "com.unity.modules.animation": "1.0.0",
    "com.unity.modules.assetbundle": "1.0.0",
    "com.unity.modules.audio": "1.0.0",
    "com.unity.modules.cloth": "1.0.0",
    "com.unity.modules.director": "1.0.0",
    "com.unity.modules.imageconversion": "1.0.0",
    "com.unity.modules.imgui": "1.0.0",
    "com.unity.modules.jsonserialize": "1.0.0",
    "com.unity.modules.particlesystem": "1.0.0",
    "com.unity.modules.physics": "1.0.0",
    "com.unity.modules.physics2d": "1.0.0",
    "com.unity.modules.screencapture": "1.0.0",
    "com.unity.modules.terrain": "1.0.0",
    "com.unity.modules.terrainphysics": "1.0.0",
    "com.unity.modules.tilemap": "1.0.0",
    "com.unity.modules.ui": "1.0.0",
    "com.unity.modules.uielements": "1.0.0",
    "com.unity.modules.umbra": "1.0.0",
    "com.unity.modules.unityanalytics": "1.0.0",
    "com.unity.modules.unitywebrequest": "1.0.0",
    "com.unity.modules.unitywebrequestassetbundle": "1.0.0",
    "com.unity.modules.unitywebrequestaudio": "1.0.0",
    "com.unity.modules.unitywebrequesttexture": "1.0.0",
    "com.unity.modules.unitywebrequestwww": "1.0.0",
    "com.unity.modules.vehicles": "1.0.0",
    "com.unity.modules.video": "1.0.0",
    "com.unity.modules.vr": "1.0.0",
    "com.unity.modules.wind": "1.0.0",
    "com.unity.modules.xr": "1.0.0"
  }
}