WindowServer: Don't ignore MouseMove events for pressed window buttons

Without this change, window buttons would get stuck in the "pressed"
state as long as the left mouse button was pressed, even if you moved
the mouse cursor out of the button rect.

Userland/Services/WindowServer/Button.cpp

@@ -56,7 +56,7 @@ void Button::on_mouse_event(const MouseEvent& event)
         break;
     }
 
-    if (!interesting_button)
+    if (event.type() != Event::Type::MouseMove && !interesting_button)
         return;
 
     auto& wm = WindowManager::the();