feat: add Window::is_decorated (#2172)

* feat: add `Window::is_decorated`

* move it right after `set_decorations`

src/platform_impl/linux/wayland/window/mod.rs

@@ -348,6 +348,11 @@ impl Window {
         self.send_request(WindowRequest::Decorate(decorate));
     }
 
+    #[inline]
+    pub fn is_decorated(&self) -> bool {
+        true
+    }
+
     #[inline]
     pub fn set_minimized(&self, minimized: bool) {
         // You can't unminimize the window on Wayland.