Make naming consistent.

src/Avalonia.Animation/TransitionInstance.cs

@@ -13,13 +13,13 @@ namespace Avalonia.Animation
     /// <summary>
     /// Handles the timing and lifetime of a <see cref="Transition{T}"/>.
     /// </summary>
-    internal class TransitionIteration : SingleSubscriberObservableBase<double>
+    internal class TransitionInstance : SingleSubscriberObservableBase<double>
     {
         private IDisposable timerSubscription;
         private TimeSpan startTime;
         private TimeSpan duration;
 
-        public TransitionIteration(TimeSpan Duration)
+        public TransitionInstance(TimeSpan Duration)
         {
             duration = Duration;
         }

src/Avalonia.Animation/Transition`1.cs

@@ -51,7 +51,7 @@ namespace Avalonia.Animation
         /// <inheritdocs/>
         public virtual IDisposable Apply(Animatable control, object oldValue, object newValue)
         {
-            var transition = DoTransition(new TransitionIteration(Duration), (T)oldValue, (T)newValue);
+            var transition = DoTransition(new TransitionInstance(Duration), (T)oldValue, (T)newValue);
             return control.Bind<T>((AvaloniaProperty<T>)Property, transition, Data.BindingPriority.Animation);
         }