Wayland, Windows, MacOS: Popup Implementation (#4543)

Implement proper decorationless popups by specifying the type of the child window with with_type()

With this commit, different kind of child windows can be created

-  Popups: Special windows without any decoration which can be positioned relative to the parent
-  Window: Normal window with a parent or not

The type can be specified during creation of the Window using the window_attributes and the with_type() function. As default a normal Window is used. If Popup is choosen a parent must be specified, otherwise the Popup creation fails with an Error returned by the new() function.

Related issues: #403 and #4256

winit-orbital/src/window.rs

@@ -37,6 +37,12 @@ impl Window {
         el: &ActiveEventLoop,
         attrs: window::WindowAttributes,
     ) -> Result<Self, RequestError> {
+        if attrs.window_type() == window::WindowType::Popup {
+            return Err(RequestError::NotSupported(NotSupportedError::new(
+                "Popups are not implemented for Orbital",
+            )));
+        }
+
         let scale = 1.;
 
         let (x, y) = if let Some(pos) = attrs.position {
@@ -154,6 +160,10 @@ impl Window {
 }
 
 impl CoreWindow for Window {
+    fn window_type(&self) -> window::WindowType {
+        window::WindowType::Window
+    }
+
     fn id(&self) -> WindowId {
         WindowId::from_raw(self.window_socket.fd())
     }