Feature Request: AdImpression event

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Checklist

• [+ ] I've updated to the latest released version of the SDK
• [ +] I've searched for existing feature requests on GitHub issues
• [ +] I've read the Code of Conduct
• [ +] I've given my issue the title: Feature Request: [name of my feature request]

Goals

I want to send "ad_impression" events (and the value of this impression) to Facebook Ads when I show an ad to a user in my app to calculate the total value for an Ad Campaign

Expected Results

I want to see a constant to the AppEventName class Presumably in this file https://github.com/facebook/facebook-sdk-for-unity/blob/main/Facebook.Unity/AppEventName.cs

For example, for Android/iOS/Web there is already such a constant called EVENT_NAME_AD_IMPRESSION. But for Unity there is no such constant: https://developers.facebook.com/docs/app-events/reference/

Code Samples & Details

I want to use it like this:

var params = new Dictionary<string, object>();
params[AppEventParameterName.AdImpressionValue] = value;
FB.LogAppEvent(AppEventName.AdImpression, parameters: params);