updated test and xml doc

com.unity.perception/Runtime/GroundTruth/Labelers/KeyPointLabeler.cs

             /// </summary>
             public float y;
             /// <summary>
-            /// The state of the point, 0 = not present, 1 = keypoint is present
+            /// The state of the point,
+            /// 0 = not present,
+            /// 1 = keypoint is present but not visible,
+            /// 2 = keypoint is present and visible
             /// </summary>
             public int state;
         }

com.unity.perception/Tests/Runtime/GroundTruthTests/KeyPointGroundTruthTests.cs

             Assert.AreEqual(t.keypoints[5].y, t.keypoints[6].y);
 
             for (var i = 0; i < 9; i++) Assert.AreEqual(i, t.keypoints[i].index);
-            for (var i = 0; i < 8; i++) Assert.AreEqual(1, t.keypoints[i].state);
+            for (var i = 0; i < 8; i++) Assert.AreEqual(2, t.keypoints[i].state);
             Assert.Zero(t.keypoints[8].state);
             Assert.Zero(t.keypoints[8].x);
             Assert.Zero(t.keypoints[8].y);