[controls] fix memory leak with Grid Row/ColumnDefinitions

src/Controls/src/Core/DefinitionCollection.cs

@@ -7,6 +7,7 @@ namespace Microsoft.Maui.Controls
 {
 	public class DefinitionCollection<T> : IList<T>, ICollection<T> where T : IDefinition
 	{
+		readonly WeakEventManager _weakEventManager = new WeakEventManager();
 		readonly List<T> _internalList;
 
 		internal DefinitionCollection() => _internalList = new List<T>();
@@ -101,13 +102,15 @@ public void RemoveAt(int index)
 			OnItemSizeChanged(this, EventArgs.Empty);
 		}
 
-		public event EventHandler ItemSizeChanged;
+		public event EventHandler ItemSizeChanged
+		{
+			add => _weakEventManager.AddEventHandler(value);
+			remove => _weakEventManager.RemoveEventHandler(value);
+		}
 
 		void OnItemSizeChanged(object sender, EventArgs e)
 		{
-			EventHandler eh = ItemSizeChanged;
-			if (eh != null)
-				eh(this, EventArgs.Empty);
+			_weakEventManager.HandleEvent(this, e, nameof(ItemSizeChanged));
 		}
 	}
 }

src/Controls/tests/Core.UnitTests/Layouts/GridLayoutTests.cs

@@ -1,4 +1,6 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
 using NSubstitute;
 using Xunit;
 
@@ -184,5 +186,45 @@ public void ColumnDefinitionsGetBindingContext()
 
 			Assert.Equal(def2.BindingContext, context);
 		}
+
+		[Fact]
+		public async Task ColumnDefinitionDoesNotLeak()
+		{
+			// Long-lived column, like from a Style in App.Resources
+			var column = new ColumnDefinition();
+			WeakReference reference;
+
+			{
+				var grid = new Grid();
+				grid.ColumnDefinitions.Add(column);
+				reference = new(grid);
+			}
+
+			await Task.Yield();
+			GC.Collect();
+			GC.WaitForPendingFinalizers();
+
+			Assert.False(reference.IsAlive, "Grid should not be alive!");
+		}
+
+		[Fact]
+		public async Task RowDefinitionDoesNotLeak()
+		{
+			// Long-lived row, like from a Style in App.Resources
+			var row = new RowDefinition();
+			WeakReference reference;
+
+			{
+				var grid = new Grid();
+				grid.RowDefinitions.Add(row);
+				reference = new(grid);
+			}
+
+			await Task.Yield();
+			GC.Collect();
+			GC.WaitForPendingFinalizers();
+
+			Assert.False(reference.IsAlive, "Grid should not be alive!");
+		}
 	}
 }