perf: Use ArrayPool<T> for Grid's CellCacheStackVector inner storage

Author: jeromelaban

src/Uno.Foundation/Collections/StackVector.cs

@@ -2,6 +2,7 @@
 using System.Collections;
 using System.Collections.Generic;
 using System.Diagnostics;
+using Uno.Buffers;
 
 namespace Uno.Collections
 {
@@ -10,10 +11,11 @@ internal class StackVector<T> : IEnumerable<T> where T : struct
 		internal delegate bool RefPredicateDelegate(ref T item);
 
 		private Memory<T> _inner;
+		private T[] _originalArray;
 
 		public StackVector(int capacity, int initialLength = 0)
 		{
-			_inner = new Memory<T>(new T[capacity]);
+			AllocateInner(capacity);
 			Count = initialLength;
 		}
 
@@ -34,15 +36,32 @@ public void Resize(int newCount)
 				// list.
 				// The resize takes place only to reuse the working
 				// memory, not to store it.
-
-				_inner = new Memory<T>(new T[newCount]);
+				AllocateInner(newCount);
 
 				IncrementResizeCount();
 			}
 
 			Count = newCount;
 		}
 
+		private void AllocateInner(int newSize)
+		{
+			if (_originalArray != null)
+			{
+				ArrayPool<T>.Shared.Return(_originalArray, clearArray: true);
+			}
+
+			_inner = new Memory<T>(_originalArray = ArrayPool<T>.Shared.Rent(newSize));
+		}
+
+		public void Dispose()
+		{
+			if (_originalArray != null)
+			{
+				ArrayPool<T>.Shared.Return(_originalArray, clearArray: true);
+			}
+		}
+
 #if DEBUG
 		internal int _numberOfResizes;
 		internal static int _totalNumberOfResizes;

src/Uno.UI/UI/Xaml/Controls/Grid/Grid.cs

@@ -444,6 +444,9 @@ void MeasureCellsGroup(
 
 			// Cleanup
 			// return hr;
+
+			// Return allocated memory to the pool
+			spanStore.Dispose();
 		}
 
 		// Measure a child of the Grid by taking in consideration the properties of
@@ -1324,6 +1327,9 @@ private XSIZEF InnerMeasureOverride(XSIZEF availableSize)
 
 				desiredSize.Width = GetDesiredInnerSize(m_pColumns) + combinedColumnSpacing;
 				desiredSize.Height = GetDesiredInnerSize(m_pRows) + combinedRowSpacing;
+
+				// Return memory to the array pool
+				cellCacheVector.Dispose();
 			}
 
 			desiredSize.Width += combinedThickness.Width;