[Text] Add textblocks virtualization benchmark, rename field

src/Avalonia.Base/Media/TextFormatting/ShapedBuffer.cs

@@ -8,12 +8,12 @@ namespace Avalonia.Media.TextFormatting
     public sealed class ShapedBuffer : IList<GlyphInfo>, IDisposable
     {
         private static readonly IComparer<GlyphInfo> s_clusterComparer = new CompareClusters();
-        private bool _rented;
+        private bool _bufferRented;
         
         public ShapedBuffer(CharacterBufferRange characterBufferRange, int bufferLength, IGlyphTypeface glyphTypeface, double fontRenderingEmSize, sbyte bidiLevel) : 
             this(characterBufferRange, ArrayPool<GlyphInfo>.Shared.Rent(bufferLength), glyphTypeface,  fontRenderingEmSize,  bidiLevel)
         {
-            _rented = true;
+            _bufferRented = true;
             Length = bufferLength;
         }
 
@@ -268,7 +268,7 @@ namespace Avalonia.Media.TextFormatting
         public void Dispose()
         {
             GC.SuppressFinalize(this);
-            if (_rented)
+            if (_bufferRented)
             {
                 GlyphInfos.ReturnRent();
             }
@@ -276,7 +276,7 @@ namespace Avalonia.Media.TextFormatting
 
         ~ShapedBuffer()
         {
-            if (_rented)
+            if (_bufferRented)
             {
                 GlyphInfos.ReturnRent();
             }

tests/Avalonia.Benchmarks/Text/HugeTextLayout.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Linq;
+using Avalonia.Controls;
 using Avalonia.Media;
 using Avalonia.Media.TextFormatting;
 using Avalonia.UnitTests;
@@ -70,6 +71,26 @@ In respect that the structure of the sufficient amount poses problems and challe
     [Benchmark]
     public TextLayout[] BuildManySmallTexts() => _manySmallStrings.Select(MakeLayout).ToArray();
 
+    [Benchmark]
+    public void VirtualizeTextBlocks()
+    {
+        var blocks = new TextBlock[10];
+        for (var i = 0; i < blocks.Length; i++)
+        {
+            blocks[i] = new TextBlock
+            {
+                Width = 120,
+                Height = 32,
+            };
+        }
+
+        for (int i = 0, j = 0; i < _manySmallStrings.Length; i++, j = j < blocks.Length - 1 ? j + 1 : 0)
+        {
+            blocks[j].Text = _manySmallStrings[i];
+            blocks[j].Measure(new Size(200, 200));
+        }
+    }
+
     private static TextLayout MakeLayout(string str)
     {
         var layout = new TextLayout(str, Typeface.Default, 12d, Brushes.Black, maxWidth: 120);