feat(pointers): Update skia hosts init to unify pointer support

src/Uno.UI.Runtime.Skia.Gtk/GtkHost.cs

@@ -107,6 +107,7 @@ public void Run()
 			SetupTheme();
 
 			ApiExtensibility.Register(typeof(Uno.ApplicationModel.Core.ICoreApplicationExtension), o => new CoreApplicationExtension(o));
+			ApiExtensibility.Register(typeof(Windows.UI.Core.IUnoCorePointerInputSource), o => new GtkCorePointerInputSource());
 			ApiExtensibility.Register(typeof(Windows.UI.Core.ICoreWindowExtension), o => new GtkCoreWindowExtension(o));
 			ApiExtensibility.Register(typeof(Windows.UI.ViewManagement.IApplicationViewExtension), o => new GtkApplicationViewExtension(o));
 			ApiExtensibility.Register(typeof(ISystemThemeHelperExtension), o => new GtkSystemThemeHelperExtension(o));
@@ -351,16 +352,17 @@ void Update()
 
 		private void OnCoreWindowContentRootSet(object sender, object e)
 		{
-			var xamlRoot = CoreServices.Instance
+			var contentRoot = CoreServices.Instance
 				.ContentRootCoordinator
-				.CoreWindowContentRoot?
-				.GetOrCreateXamlRoot();
+				.CoreWindowContentRoot;
+			var xamlRoot = contentRoot?.GetOrCreateXamlRoot();
 
 			if (xamlRoot is null)
 			{
 				throw new InvalidOperationException("XamlRoot was not properly initialized");
 			}
 
+			contentRoot!.SetHost(this);
 			XamlRootMap.Register(xamlRoot, this);
 			xamlRoot.InvalidateRender += _renderSurface.InvalidateRender;
 

src/Uno.UI.Runtime.Skia.Gtk/Hosting/XamlRootMap.cs

@@ -24,6 +24,7 @@ internal static void Register(XamlRoot xamlRoot, GtkHost host)
 		}
 
 		_map[xamlRoot] = host;
+		xamlRoot.VisualTree.ContentRoot.SetHost(host); // Note: This might be a duplicated call but it's supported by ContentRoot and safe
 
 		xamlRoot.InvalidateRender += host.RenderSurface.InvalidateRender;
 	}

src/Uno.UI.Runtime.Skia.Linux.FrameBuffer/CoreWindowExtension.Keyboard.cs

@@ -69,7 +69,7 @@ private void OnKeyPressEvent(libinput_key key)
 					RepeatCount = 1,
 				});
 
-			RaiseKeyEvent(_ownerEvents.RaiseNativeKeyDownReceived, args);
+			RaiseKeyEvent(_owner.RaiseNativeKeyDownReceived, args);
 		}
 
 		private void OnKeyReleaseEvent(libinput_key key)
@@ -92,7 +92,7 @@ private void OnKeyReleaseEvent(libinput_key key)
 					RepeatCount = 1,
 				});
 
-			RaiseKeyEvent(_ownerEvents.RaiseNativeKeyUpReceived, args);
+			RaiseKeyEvent(_owner.RaiseNativeKeyUpReceived, args);
 		}
 
 		private void RaiseKeyEvent(Action<KeyEventArgs> raisePointerEvent, KeyEventArgs args)