Add IImageBrushSource.GetBitmap(), update build/api suppressions (#21638)

* Expose IRef/IImageBrushSource, update build/api suppressions

* Hide IRef from image brush source API

Internalized `IRef<T>` and removed it from the `IImageBrushSource` public surface by making `Bitmap` internal. Added a `[PrivateApi]` `GetBitmap()` helper returning `IBitmapImpl?` so internal consumers can still access the bitmap without exposing ref-count internals. Updated Skia drawing code to use `GetBitmap()` and refreshed API suppression entries accordingly.

Directory.Build.props

@@ -10,6 +10,8 @@
     <LangVersion>14.0</LangVersion>
     <TreatWarningsAsErrors Condition="'$(TreatWarningsAsErrors)' == ''">$(AvnTreatWarningsAsErrors)</TreatWarningsAsErrors>
     <TreatWarningsAsErrors Condition="'$(TreatWarningsAsErrors)' == '' And '$(Configuration)' == 'Release'">true</TreatWarningsAsErrors>
+    <!-- Suppress NU1507 so local source builds do not warn about the consuming solution's package sources. -->
+    <NoWarn>$(NoWarn);NU1507</NoWarn>
     <CreateHardLinksForCopyAdditionalFilesIfPossible>true</CreateHardLinksForCopyAdditionalFilesIfPossible>
     <CreateHardLinksForCopyFilesToOutputDirectoryIfPossible>true</CreateHardLinksForCopyFilesToOutputDirectoryIfPossible>
     <CreateHardLinksForCopyLocalIfPossible>true</CreateHardLinksForCopyLocalIfPossible>

api/Avalonia.nupkg.xml

@@ -157,6 +157,12 @@
     <Left>baseline/Avalonia/lib/net10.0/Avalonia.Base.dll</Left>
     <Right>current/Avalonia/lib/net10.0/Avalonia.Base.dll</Right>
   </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0006</DiagnosticId>
+    <Target>P:Avalonia.Media.IImageBrushSource.Bitmap</Target>
+    <Left>baseline/Avalonia/lib/net10.0/Avalonia.Base.dll</Left>
+    <Right>current/Avalonia/lib/net10.0/Avalonia.Base.dll</Right>
+  </Suppression>
   <Suppression>
     <DiagnosticId>CP0006</DiagnosticId>
     <Target>M:Avalonia.Controls.Platform.IWin32OptionsTopLevelImpl.SetWindowCornerPreference(Avalonia.Controls.Win32Properties.WindowCornerPreference)</Target>
@@ -181,6 +187,12 @@
     <Left>baseline/Avalonia/lib/net8.0/Avalonia.Base.dll</Left>
     <Right>current/Avalonia/lib/net8.0/Avalonia.Base.dll</Right>
   </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0006</DiagnosticId>
+    <Target>P:Avalonia.Media.IImageBrushSource.Bitmap</Target>
+    <Left>baseline/Avalonia/lib/net8.0/Avalonia.Base.dll</Left>
+    <Right>current/Avalonia/lib/net8.0/Avalonia.Base.dll</Right>
+  </Suppression>
   <Suppression>
     <DiagnosticId>CP0006</DiagnosticId>
     <Target>M:Avalonia.Controls.Platform.IWin32OptionsTopLevelImpl.SetWindowCornerPreference(Avalonia.Controls.Win32Properties.WindowCornerPreference)</Target>

src/Avalonia.Base/Media/IImageBrush.cs

@@ -17,9 +17,21 @@ namespace Avalonia.Media
         IImageBrushSource? Source { get; }
     }
 
+    /// <summary>
+    /// Provides access to the image source of an <see cref="IImageBrush"/>. 
+    /// </summary>
     [NotClientImplementable]
     public interface IImageBrushSource
     {
         internal IRef<IBitmapImpl>? Bitmap { get; }
+
+        /// <summary>
+        /// Gets the bitmap implementation of the image source.
+        /// </summary>
+        /// <returns>
+        /// The <see cref="IBitmapImpl"/> instance if available; otherwise, <c>null</c>.
+        /// </returns>
+        [PrivateApi]
+        IBitmapImpl? GetBitmap() => Bitmap?.Item;
     }
 }

src/Avalonia.Base/Utilities/Ref.cs

@@ -7,7 +7,11 @@ namespace Avalonia.Utilities
     /// <summary>
     /// A ref-counted wrapper for a disposable object.
     /// </summary>
-    /// <typeparam name="T"></typeparam>
+    /// <typeparam name="T">
+    /// The type of the item being ref-counted. 
+    /// Must be a reference type to avoid issues with copying value types and must be disposable
+    /// to ensure the item is cleaned up when the refcount reaches 0.
+    /// </typeparam>
     internal interface IRef<out T> : IDisposable where T : class
     {
         /// <summary>

src/Skia/Avalonia.Skia/DrawingContextImpl.cs

@@ -1428,7 +1428,7 @@ namespace Avalonia.Skia
             }
             else
             {
-                tileBrushImage = (tileBrush as IImageBrush)?.Source?.Bitmap?.Item as IDrawableBitmapImpl;
+                tileBrushImage = (tileBrush as IImageBrush)?.Source?.GetBitmap() as IDrawableBitmapImpl;
             }
 
             if (tileBrush != null && tileBrushImage != null)