fix(listview): [Android] Fix flicker and clipping when ListViewItem.M…

…argin is set

Fix a regression introduced by performance improvements to reduce the number of times items are measured. The margin was being omitted, leading to strange results.

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml_Controls/Given_ListViewBase.Measure.cs

@@ -6,6 +6,7 @@
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using Windows.UI.Xaml;
 using Windows.UI.Xaml.Controls;
+using Uno.UI.RuntimeTests.Extensions;
 #if NETFX_CORE
 using Uno.UI.Extensions;
 #elif __IOS__
@@ -309,6 +310,40 @@ private static void ScrollBy(ListViewBase listViewBase, double scrollBy)
 			sv.ChangeView(null, scrollBy, null);
 		}
 
+		private static async Task ScrollByInIncrements(ListViewBase listViewBase, double scrollBy)
+		{
+			var sv = listViewBase.FindFirstChild<ScrollViewer>();
+			Assert.IsNotNull(sv);
+			var current = sv.VerticalOffset;
+			if (current == scrollBy)
+			{
+				return;
+			}
+			var increment = sv.ActualHeight / 2;
+			if (increment == 0)
+			{
+				Assert.Fail("ScrollViewer must have non-zero height");
+			}
+			if (scrollBy > current)
+			{
+				for (double d = current + increment; d < scrollBy; d += increment)
+				{
+					sv.ChangeView(null, d, null);
+					await Task.Delay(10);
+				}
+			}
+			else
+			{
+				for (double d = current - increment; d > scrollBy; d -= increment)
+				{
+					sv.ChangeView(null, d, null);
+					await Task.Delay(10);
+				}
+			}
+
+			sv.ChangeView(null, scrollBy, null);
+		}
+
 		public class When_Item_Changes_Measure_Count_ItemViewModel : System.ComponentModel.INotifyPropertyChanged
 		{
 

src/Uno.UI/UI/Xaml/Controls/ListViewBase/VirtualizingPanelLayout.Android.cs

@@ -984,7 +984,19 @@ private Size TryMeasureChild(View child, Size slotSize, ViewType viewType)
 			}
 			else
 			{
-				return (child as FrameworkElement)?.AssignedActualSize ?? ViewHelper.PhysicalToLogicalPixels(new Size(child.Width, child.Height));
+				return GetMeasuredChildSize(child);
+			}
+		}
+
+		private static Size GetMeasuredChildSize(View child)
+		{
+			if (child is FrameworkElement fe)
+			{
+				return fe.AssignedActualSize.Add(fe.Margin);
+			}
+			else
+			{
+				return ViewHelper.PhysicalToLogicalPixels(new Size(child.Width, child.Height));
 			}
 		}