Implement SetMode and FetchMode window actions

native/src/window/mode.rs

@@ -0,0 +1,12 @@
+/// The mode of a window-based application.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Mode {
+    /// The application appears in its own window.
+    Windowed,
+
+    /// The application takes the whole screen of its current monitor.
+    Fullscreen,
+
+    /// The application is hidden
+    Hidden,
+}