Add a pooled option in BindingExpressionGrammar.

Micro-optimization.

src/Markup/Avalonia.Markup/Data/Binding.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
+using Avalonia.Collections.Pooled;
 using Avalonia.Controls;
 using Avalonia.Data.Converters;
 using Avalonia.Data.Core;
@@ -104,7 +105,7 @@ namespace Avalonia.Data
             if (!string.IsNullOrEmpty(Path))
             {
                 var reader = new CharacterReader(Path.AsSpan());
-                var (astNodes, sourceMode) = BindingExpressionGrammar.Parse(ref reader);
+                var (astNodes, sourceMode) = BindingExpressionGrammar.ParseToPooledList(ref reader);
                 nodes = ExpressionNodeFactory.CreateFromAst(
                     astNodes,
                     TypeResolver,
@@ -137,9 +138,9 @@ namespace Avalonia.Data
             if (!string.IsNullOrEmpty(Path))
             {
                 var reader = new CharacterReader(Path.AsSpan());
-                var (astNodes, sourceMode) = BindingExpressionGrammar.Parse(ref reader);
+                var (astPool, sourceMode) = BindingExpressionGrammar.ParseToPooledList(ref reader);
                 nodes = ExpressionNodeFactory.CreateFromAst(
-                    astNodes,
+                    astPool,
                     TypeResolver,
                     GetNameScope(),
                     out isRooted);

src/Markup/Avalonia.Markup/Markup/Parsers/BindingExpressionGrammar.cs

@@ -16,9 +16,26 @@ namespace Avalonia.Markup.Parsers
 
     internal static class BindingExpressionGrammar
     {
+        private static readonly List<INode> s_pool = new();
+
         public static (List<INode> Nodes, SourceMode Mode) Parse(ref CharacterReader r)
         {
-            var nodes = new List<INode>();
+            var result = new List<INode>();
+            var mode = Parse(ref r, result);
+            return (result, mode);
+        }
+
+        public static (List<INode> Nodes, SourceMode Mode) ParseToPooledList(ref CharacterReader r)
+        {
+            // Most of the time the list will be passed to `ExpressionNodeFactory.CreateFromAst`
+            // and then discarded so as a micro-optimization we can reuse the list.
+            s_pool.Clear();
+            var mode = Parse(ref r, s_pool);
+            return (s_pool, mode);
+        }
+
+        private static SourceMode Parse(ref CharacterReader r, List<INode> nodes)
+        {
             var state = State.Start;
             var mode = SourceMode.Data;
 
@@ -72,7 +89,7 @@ namespace Avalonia.Markup.Parsers
                 throw new ExpressionParseException(r.Position, "Unexpected end of expression.");
             }
 
-            return (nodes, mode);
+            return mode;
         }
 
         private static State ParseStart(ref CharacterReader r, IList<INode> nodes)