missing Microsoft Xbox's build targets (using in 2020.3.x and higher)

[am1goo]

Checklist

• I've updated to the latest released version of the SDK
• I've searched for existing GitHub issues
• I've looked for existing answers on Stack Overflow, the Facebook Developer Community Forum and the Facebook Developers Group
• I've read the Code of Conduct
• This issue is not security related and can safely be disclosed publicly on GitHub

Environment

Describe your dev environment here, giving as many details as possible. If you have them, make sure to include:

• Unity Editor Version: 2020.3.48f1
• Unity SDK Version: 16.0.2
• Installation Platform & Verison: GameCoreScarlett|GameCoreXboxSeries|GameCoreXboxOne version 2020.3.48f1

Goals

Playing mode should be starter without any parsing errors in console

Expected Results

No parsing errors about Facebook.Unity.Settings.BuildTarget missing values

Actual Results

Exception about Facebook.Unity.Settings.BuildTarget missing values

ArgumentException: Requested value 'GameCoreScarlett' was not found.
System.Enum+EnumResult.SetFailure (System.Enum+ParseFailureKind failure, System.String failureMessageID, System.Object failureMessageFormatArgument) (at <695d1cc93cca45069c528c15c9fdd749>:0)
System.Enum.TryParseEnum (System.Type enumType, System.String value, System.Boolean ignoreCase, System.Enum+EnumResult& parseResult) (at <695d1cc93cca45069c528c15c9fdd749>:0)
System.Enum.Parse (System.Type enumType, System.String value, System.Boolean ignoreCase) (at <695d1cc93cca45069c528c15c9fdd749>:0)
Facebook.Unity.Editor.PlayModeStateChanged.OnPlayModeStateChange (UnityEditor.PlayModeStateChange state) (at <d94eaa45a06f4a28b0b54293a88028d7>:0)
UnityEditor.EditorApplication.Internal_PlayModeStateChanged (UnityEditor.PlayModeStateChange state) (at <25578071f6e44201aac745680e5c8dfc>:0)

Steps to Reproduce

1. get XBOX@ID account
2. download and install Xbox GameCore module, install latest version of Facebook SDK for Unity
3. run project with empty scene

Code Samples & Details

public enum BuildTarget
{
    StandaloneOSX,
    StandaloneWindows,
    iOS,
    Android,
    StandaloneWindows64,
    WebGL,
    WSAPlayer,
    StandaloneLinux64,
    PS4,
    XboxOne,
    tvOS,
    Switch,
    Stadia,
    CloudRendering,
    PS5,
    none,
    GameCoreScarlett, //<-- missing value
    GameCoreXboxSeries, //<-- missing value
    GameCoreXboxOne, //<-- missing value
}

[am1goo]

I've made Pull Request with fix #710