feat: add Window::is_resizable (#2171)

* feat: add `Window::is_resizable`

* move it right after `set_resizable`

src/platform_impl/linux/x11/window.rs

@@ -1211,6 +1211,11 @@ impl UnownedWindow {
         .expect("Failed to call `XSetWMNormalHints`");
     }
 
+    #[inline]
+    pub fn is_resizable(&self) -> bool {
+        true
+    }
+
     #[inline]
     pub fn xlib_display(&self) -> *mut c_void {
         self.xconn.display as _