Make DelayedBinding internal.

Is only used by `StaticResource` and a few unit tests. Can probably be removed.

src/Markup/Avalonia.Markup/Avalonia.Markup.csproj

@@ -19,7 +19,9 @@
   <Import Project="..\..\..\build\TrimmingEnable.props" />
 
   <ItemGroup Label="InternalsVisibleTo">
+    <InternalsVisibleTo Include="Avalonia.Controls.UnitTests, PublicKey=$(AvaloniaPublicKey)" />
     <InternalsVisibleTo Include="Avalonia.Markup.Xaml, PublicKey=$(AvaloniaPublicKey)" />
     <InternalsVisibleTo Include="Avalonia.Markup.UnitTests, PublicKey=$(AvaloniaPublicKey)" />
+    <InternalsVisibleTo Include="Avalonia.Markup.Xaml.UnitTests, PublicKey=$(AvaloniaPublicKey)" />
   </ItemGroup>
 </Project>

src/Markup/Avalonia.Markup/Markup/Data/DelayedBinding.cs

@@ -18,7 +18,7 @@ namespace Avalonia.Markup.Data
     /// is applied to the property before the properties on the `Binding` object are set. Looking 
     /// at WPF it uses a similar mechanism for bindings that come from XAML.
     /// </remarks>
-    public static class DelayedBinding
+    internal static class DelayedBinding
     {
         private static readonly ConditionalWeakTable<StyledElement, List<Entry>> _entries = new();