Fixed creating RenderTarget when using Vulkan backend (#20952)

* Updated VulkanContext.TryGetFeature to also provide IVulkanKhrSurfacePlatformSurfaceFactory
This also fixed creating new RenderTarget when using Vulkan backend, see issue #20824

* Prevent duplicate check if _renderTarget is null

src/Avalonia.Base/Rendering/Composition/Server/ServerCompositionTarget.cs

@@ -149,12 +149,16 @@ namespace Avalonia.Rendering.Composition.Server
 
             try
             {
-                if (_renderTarget == null && !_compositor.IsReadyToCreateRenderTarget(_surfaces()))
+                if (_renderTarget == null)
+                {
+                    if (!_compositor.IsReadyToCreateRenderTarget(_surfaces()))
                     {
                         IsWaitingForReadyRenderTarget = IsEnabled;
                         return;
                     }
-                _renderTarget ??= _compositor.CreateRenderTarget(_surfaces());
+
+                    _renderTarget = _compositor.CreateRenderTarget(_surfaces());
+                }
             }
             catch (RenderTargetNotReadyException)
             {

src/Avalonia.Vulkan/VulkanContext.cs

@@ -41,6 +41,10 @@ internal class VulkanContext : IVulkanPlatformGraphicsContext
     {
         if (featureType == typeof(IVulkanContextExternalObjectsFeature))
             return _externalObjectsFeature;
+                
+        if (featureType == typeof(IVulkanKhrSurfacePlatformSurfaceFactory))
+            return _surfaceFactory;
+
         return null;
     }