Improve measure invalidation and legacy Layout(s) performance

- Do not bubble up `MeasureInvalidated` on scrollable views and pages
- Do not synchronously measure/arrange children on legacy layout upon child measure invalidated: simply wait for the next native layout pass

src/Controls/src/Core/Items/ItemsView.cs

@@ -224,5 +224,10 @@ protected override void OnBindingContextChanged()
  if (InternalItemsLayout is BindableObject bo)
  SetInheritedBindingContext(bo, BindingContext);
  }
+
+ internal override void OnChildMeasureInvalidatedInternal(VisualElement child, InvalidationTrigger trigger)
+ {
+ // No need to trigger and propagate MeasureInvalidated given this is a scrollable area
+ }
  }
 }

src/Controls/src/Core/ItemsView.cs

@@ -85,5 +85,10 @@ static void OnItemsSourceChanged(BindableObject bindable, object oldValue, objec
  }
 
  protected virtual bool ValidateItemTemplate(DataTemplate template) => true;
+
+ internal override void OnChildMeasureInvalidatedInternal(VisualElement child, InvalidationTrigger trigger)
+ {
+ // No need to trigger and propagate MeasureInvalidated given this is a scrollable area
+ }
  }
 }

src/Controls/src/Core/LegacyLayouts/Layout.cs

@@ -321,6 +321,8 @@ protected virtual void InvalidateLayout()
 
  internal override void OnChildMeasureInvalidatedInternal(VisualElement child, InvalidationTrigger trigger)
  {
+ base.OnChildMeasureInvalidatedInternal(child, trigger);
+
  // TODO: once we remove old Xamarin public signatures we can invoke `OnChildMeasureInvalidated(VisualElement, InvalidationTrigger)` directly
  OnChildMeasureInvalidated(child, new InvalidationEventArgs(trigger));
  }
@@ -503,7 +505,7 @@ internal virtual void OnChildMeasureInvalidated(VisualElement child, Invalidatio
  int count = children.Count;
  for (var index = 0; index < count; index++)
  {
- if (LogicalChildrenInternal[index] is VisualElement v && v.IsVisible && (!v.IsPlatformEnabled || !v.IsPlatformStateConsistent))
+ if (LogicalChildrenInternal[index] is VisualElement { IsVisible: true } v && (!v.IsPlatformEnabled || !v.IsPlatformStateConsistent))
  {
  return;
  }
@@ -517,20 +519,13 @@ internal virtual void OnChildMeasureInvalidated(VisualElement child, Invalidatio
  {
  return;
  }
- if (trigger == InvalidationTrigger.HorizontalOptionsChanged || trigger == InvalidationTrigger.VerticalOptionsChanged)
+ if (trigger is InvalidationTrigger.HorizontalOptionsChanged or InvalidationTrigger.VerticalOptionsChanged)
  {
  ComputeConstraintForView(view);
  }
  }
 
- if (trigger == InvalidationTrigger.RendererReady)
- {
- InvalidateMeasureInternal(InvalidationTrigger.RendererReady);
- }
- else
- {
- InvalidateMeasureInternal(InvalidationTrigger.MeasureChanged);
- }
+ // Nothing else to do here: platform will take care of arranging the children if needed on the next layout pass
  }
 
  internal override void OnIsVisibleChanged(bool oldValue, bool newValue)

src/Controls/src/Core/Page/Page.cs

@@ -499,7 +499,7 @@ protected override void OnBindingContextChanged()
 
  internal override void OnChildMeasureInvalidatedInternal(VisualElement child, InvalidationTrigger trigger)
  {
- // TODO: once we remove old Xamarin public signatures we can invoke `OnChildMeasureInvalidated(VisualElement, InvalidationTrigger)` directly
+ // No need to trigger and propagate MeasureInvalidated considering Page is the root node
  OnChildMeasureInvalidated(child, new InvalidationEventArgs(trigger));
  }
 
@@ -510,8 +510,7 @@ internal override void OnChildMeasureInvalidatedInternal(VisualElement child, In
  /// <param name="e">The event arguments.</param>
  protected virtual void OnChildMeasureInvalidated(object sender, EventArgs e)
  {
- InvalidationTrigger trigger = (e as InvalidationEventArgs)?.Trigger ?? InvalidationTrigger.Undefined;
- OnChildMeasureInvalidated((VisualElement)sender, trigger);
+ // Nothing to do here: platform will take care of arranging the children if needed on the next layout pass
  }
 
  /// <summary>
@@ -583,29 +582,6 @@ protected void UpdateChildrenLayout()
  }
  }
 
- internal virtual void OnChildMeasureInvalidated(VisualElement child, InvalidationTrigger trigger)
- {
- var container = this as IPageContainer<Page>;
- if (container != null)
- {
- Page page = container.CurrentPage;
- if (page != null && page.IsVisible && (!page.IsPlatformEnabled || !page.IsPlatformStateConsistent))
- return;
- }
- else
- {
- var logicalChildren = this.InternalChildren;
- for (var i = 0; i < logicalChildren.Count; i++)
- {
- var v = logicalChildren[i] as VisualElement;
- if (v != null && v.IsVisible && (!v.IsPlatformEnabled || !v.IsPlatformStateConsistent))
- return;
- }
- }
-
- InvalidateMeasureInternal(InvalidationTrigger.MeasureChanged);
- }
-
  internal void OnAppearing(Action action)
  {
  if (_hasAppeared)

src/Controls/src/Core/ScrollView/ScrollView.cs

@@ -489,5 +489,10 @@ Size ICrossPlatformLayout.CrossPlatformArrange(Rect bounds)
 
  return bounds.Size;
  }
+
+ internal override void OnChildMeasureInvalidatedInternal(VisualElement child, InvalidationTrigger trigger)
+ {
+ // No need to trigger and propagate MeasureInvalidated given this is a scrollable area
+ }
  }
 }