feat(Base): Address Rule CA1823

src/Avalonia.Base/Data/Core/ExpressionNode.cs

@@ -4,8 +4,6 @@ namespace Avalonia.Data.Core
 {
     public abstract class ExpressionNode
     {
-        private static readonly object CacheInvalid = new object();
-
         protected static readonly WeakReference<object?> UnsetReference = 
             new WeakReference<object?>(AvaloniaProperty.UnsetValue);
 

src/Avalonia.Base/Data/Core/ExpressionObserver.cs

@@ -49,8 +49,6 @@ namespace Avalonia.Data.Core
                 new TaskStreamPlugin(),
                 new ObservableStreamPlugin(),
             };
-
-        private static readonly object UninitializedValue = new object();
         private readonly ExpressionNode _node;
         private object? _root;
         private Func<object?>? _rootGetter;

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

@@ -8,7 +8,6 @@ namespace Avalonia.Media.TextFormatting
     internal readonly struct FormattedTextSource : ITextSource
     {
         private readonly CharacterBufferRange _text;
-        private readonly int length;
         private readonly TextRunProperties _defaultProperties;
         private readonly IReadOnlyList<ValueSpan<TextRunProperties>>? _textModifier;
 

src/Avalonia.Base/Media/TextFormatting/Unicode/CodepointEnumerator.cs

@@ -5,7 +5,6 @@ namespace Avalonia.Media.TextFormatting.Unicode
     public ref struct CodepointEnumerator
     {
         private CharacterBufferRange _text;
-        private int _pos;
 
         public CodepointEnumerator(CharacterBufferRange text)
         {