feature: Add OnJointBreakAsObservable() trigger.

The real implementation was already there. I only added the extension
method to make it easier to access.

Assets/Plugins/UniRx/Scripts/UnityEngineBridge/Triggers/ObservableTriggerExtensions.Component.cs

@@ -457,5 +457,11 @@ public static IObservable<Unit> OnParticleTriggerAsObservable(this Component com
 #endif
 
         #endregion
+
+        public static IObservable<float> OnJointBreakAsObservable(this Joint joint)
+        {
+            if (joint == null || joint.gameObject == null) return Observable.Empty<float>();
+            return GetOrAddComponent<ObservableJointTrigger>(joint.gameObject).OnJointBreakAsObservable();
+        }
     }
-}
+}