Toplevel - Fix system theme not being applied at launch on some platforms (#16159)

* move platformbinding for theme variant from WindowBase up to TopLevel.

* remvoe visibility check in android insets manager for system theme

src/Android/Avalonia.Android/Platform/AndroidInsetsManager.cs

@@ -191,11 +191,6 @@ namespace Avalonia.Android.Platform
             {
                 _statusBarTheme = value;
 
-                if (!_topLevel.View.IsShown)
-                {
-                    return;
-                }
-
                 var compat = new WindowInsetsControllerCompat(Window, _topLevel.View);
 
                 if (_isDefaultSystemBarLightTheme == null)
@@ -229,11 +224,6 @@ namespace Avalonia.Android.Platform
             {
                 _systemUiVisibility = value;
 
-                if (!_topLevel.View.IsShown)
-                {
-                    return;
-                }
-
                 var compat = WindowCompat.GetInsetsController(Window, _topLevel.View);
 
                 if (value == null || value.Value)

src/Avalonia.Controls/TopLevel.cs

@@ -232,6 +232,11 @@ namespace Avalonia.Controls
             impl.TransparencyLevelChanged = HandleTransparencyLevelChanged;
 
             CreatePlatformImplBinding(TransparencyLevelHintProperty, hint => PlatformImpl.SetTransparencyLevelHint(hint ?? Array.Empty<WindowTransparencyLevel>()));
+            CreatePlatformImplBinding(ActualThemeVariantProperty, variant =>
+            {
+                variant ??= ThemeVariant.Default;
+                PlatformImpl?.SetFrameThemeVariant((PlatformThemeVariant?)variant ?? PlatformThemeVariant.Light);
+            });
 
             _keyboardNavigationHandler?.SetOwner(this);
             _accessKeyHandler?.SetOwner(this);

src/Avalonia.Controls/WindowBase.cs

@@ -48,11 +48,6 @@ namespace Avalonia.Controls
         public WindowBase(IWindowBaseImpl impl) : this(impl, AvaloniaLocator.Current)
         {
             CreatePlatformImplBinding(TopmostProperty, topmost => PlatformImpl!.SetTopmost(topmost));
-            CreatePlatformImplBinding(ActualThemeVariantProperty, variant =>
-            {
-                variant ??= ThemeVariant.Default;
-                PlatformImpl?.SetFrameThemeVariant((PlatformThemeVariant?)variant ?? PlatformThemeVariant.Light);
-            });
             
             FrameSize = impl.FrameSize;
         }