Merge pull request #18628 from ramezgerges/x11_window_activation

fix(x11): Window.Activate() should immediately raise the window

src/Uno.UI.Runtime.Skia.X11/X11WindowWrapper.cs

@@ -67,6 +67,7 @@ public override void Activate()
 		var x11Window = _host.RootX11Window;
 		using var lockDiposable = X11Helper.XLock(x11Window.Display);
 		_ = XLib.XRaiseWindow(x11Window.Display, x11Window.Window);
+		_ = XLib.XFlush(x11Window.Display); // Important! Otherwise X commands will sit waiting to be flushed, and since the window is not activated, there are no new X commands being sent to force a flush.
 
 		// We could send _NET_ACTIVE_WINDOW as well, although it doesn't seem to be needed (and only works with EWMH-compliant WMs)
 		// XClientMessageEvent xclient = default;