Adjust some Unstable attr usages

src/Avalonia.Base/Controls/IThemeVariantProvider.cs

@@ -10,9 +10,8 @@ namespace Avalonia.Controls;
 /// <remarks>
 /// This is a helper interface for the XAML compiler to make Key property accessibly by the markup extensions.
 /// Which means, it can only be used with ResourceDictionaries and markup extensions in the XAML code.
-/// This API might be removed in the future minor updates.
 /// </remarks>
-[Unstable]
+[Unstable("This XAML-only API might be removed in the future minor updates.")]
 public interface IThemeVariantProvider : IResourceProvider
 {
     /// <summary>

src/Avalonia.Base/Input/DragEventArgs.cs

@@ -25,8 +25,7 @@ namespace Avalonia.Input
             return _target.TranslatePoint(_targetLocation, relativeTo) ?? new Point(0, 0);
         }
 
-        [Unstable]
+        [Unstable("This constructor might be removed in 12.0. For unit testing, consider using DragDrop.DoDragDrop or IHeadlessWindow.DragDrop.")]
-        [Obsolete("This constructor might be removed in 12.0. For unit testing, consider using DragDrop.DoDragDrop or IHeadlessWindow.DragDrop.")]
         public DragEventArgs(RoutedEvent<DragEventArgs> routedEvent, IDataObject data, Interactive target, Point targetLocation, KeyModifiers keyModifiers)
             : base(routedEvent)
         {

src/Avalonia.Base/Input/PointerDeltaEventArgs.cs

@@ -9,8 +9,7 @@ namespace Avalonia.Input
     {
         public Vector Delta { get; }
 
-        [Unstable]
+        [Unstable("This constructor might be removed in 12.0.")]
-        [Obsolete("This constructor might be removed in 12.0.")]
         public PointerDeltaEventArgs(RoutedEvent routedEvent, object? source, 
             IPointer pointer, Visual rootVisual, Point rootVisualPosition, ulong timestamp,
             PointerPointProperties properties, KeyModifiers modifiers, Vector delta) 

src/Avalonia.Base/Input/PointerEventArgs.cs

@@ -14,8 +14,7 @@ namespace Avalonia.Input
         private readonly PointerPointProperties _properties;
         private readonly Lazy<IReadOnlyList<RawPointerPoint>?>? _previousPoints;
 
-        [Unstable]
+        [Unstable("This constructor might be removed in 12.0. For unit testing, consider using IHeadlessWindow mouse methods.")]
-        [Obsolete("This constructor might be removed in 12.0. For unit testing, consider using IHeadlessWindow mouse methods.")]
         public PointerEventArgs(RoutedEvent routedEvent,
             object? source,
             IPointer pointer,
@@ -129,8 +128,7 @@ namespace Avalonia.Input
 
     public class PointerPressedEventArgs : PointerEventArgs
     {
-        [Unstable]
+        [Unstable("This constructor might be removed in 12.0. For unit testing, consider using IHeadlessWindow mouse methods.")]
-        [Obsolete("This constructor might be removed in 12.0. For unit testing, consider using IHeadlessWindow mouse methods.")]
         public PointerPressedEventArgs(
             object source,
             IPointer pointer,
@@ -150,8 +148,7 @@ namespace Avalonia.Input
 
     public class PointerReleasedEventArgs : PointerEventArgs
     {
-        [Unstable]
+        [Unstable("This constructor might be removed in 12.0. For unit testing, consider using IHeadlessWindow mouse methods.")]
-        [Obsolete("This constructor might be removed in 12.0. For unit testing, consider using IHeadlessWindow mouse methods.")]
         public PointerReleasedEventArgs(
             object source, IPointer pointer,
             Visual rootVisual, Point rootVisualPosition, ulong timestamp,
@@ -173,8 +170,7 @@ namespace Avalonia.Input
     {
         public IPointer Pointer { get; }
 
-        [Unstable]
+        [Unstable("This constructor might be removed in 12.0. If you need to remove capture, use stable methods on the IPointer instance.,")]
-        [Obsolete("This constructor might be removed in 12.0. If you need to remove capture, use stable methods on the IPointer instance.,")]
         public PointerCaptureLostEventArgs(object source, IPointer pointer) : base(InputElement.PointerCaptureLostEvent)
         {
             Pointer = pointer;

src/Avalonia.Base/Input/PointerWheelEventArgs.cs

@@ -9,8 +9,7 @@ namespace Avalonia.Input
     {
         public Vector Delta { get; }
 
-        [Unstable]
+        [Unstable("This constructor might be removed in 12.0. For unit testing, consider using IHeadlessWindow.MouseWheel.")]
-        [Obsolete("This constructor might be removed in 12.0. For unit testing, consider using IHeadlessWindow.MouseWheel.")]
         public PointerWheelEventArgs(object source, IPointer pointer, Visual rootVisual,
             Point rootVisualPosition, ulong timestamp,
             PointerPointProperties properties, KeyModifiers modifiers, Vector delta)

src/Avalonia.Base/Platform/IAssetLoader.cs

@@ -9,7 +9,7 @@ namespace Avalonia.Platform
     /// <summary>
     /// Loads assets compiled into the application binary.
     /// </summary>
-    [Unstable]
+    [Unstable("IAssetLoader interface and AvaloniaLocator usage is considered unstable. Please use AssetLoader static class instead.")]
     public interface IAssetLoader
     {
         /// <summary>