Don't invalidate ItemsRepeater measure on children change.

src/Avalonia.Controls/Panel.cs

@@ -137,6 +137,11 @@ namespace Avalonia.Controls
                     throw new NotSupportedException();
             }
 
+            InvalidateMeasureOnChildrenChanged();
+        }
+
+        private protected virtual void InvalidateMeasureOnChildrenChanged()
+        {
             InvalidateMeasure();
         }
 

src/Avalonia.Controls/Repeater/ItemsRepeater.cs

@@ -267,6 +267,11 @@ namespace Avalonia.Controls
             return result;
         }
 
+        private protected override void InvalidateMeasureOnChildrenChanged()
+        {
+            // Don't invalidate measure when children change.
+        }
+
         protected override Size MeasureOverride(Size availableSize)
         {
             if (_isLayoutInProgress)