[Face Detection LandMark] Add a confidence score to the eye landmarks when wearing a black glasses

**What's your feature request? Please describe.**

Why Google mlkit face-detection can still detect mouth landmark when I wear a mask.

how can i know there are no mouth landmark when I wear a mask and
there are no eye landmark when I wear a Dark glasses ？

can we Add a confidence scores of the landmarks when face landmark is hidden by glasses mask ?

public class FaceLandmark {
private final int zza;
private final PointF zzb;
confidence score ? // flag landmark is hidden by things
.........

**Mobile environment**
Android, IOS or both

Android first

**Additional context**