desktop: Add Alt+Enter back as a hidden shortcut on Windows

Previously Alt+Enter was a hidden shortcut that was used to toggle
full screen, and it is used by Flash Player to toggle full screen
on Windows too.

As Windows users sometimes expect this shortcut to work, this
patch brings it back as a hidden shortcut (until we add some kind of preferences).

desktop/src/gui/menu_bar.rs

@@ -23,6 +23,8 @@ pub struct MenuBar {
 
 impl MenuBar {
     const SHORTCUT_FULLSCREEN: KeyboardShortcut = KeyboardShortcut::new(Modifiers::NONE, Key::F11);
+    const SHORTCUT_FULLSCREEN_WINDOWS: KeyboardShortcut =
+        KeyboardShortcut::new(Modifiers::ALT, Key::Enter);
     const SHORTCUT_OPEN: KeyboardShortcut = KeyboardShortcut::new(Modifiers::COMMAND, Key::O);
     const SHORTCUT_OPEN_ADVANCED: KeyboardShortcut =
         KeyboardShortcut::new(Modifiers::COMMAND.plus(Modifiers::SHIFT), Key::O);
@@ -64,7 +66,14 @@ impl MenuBar {
                 player.set_is_playing(!player.is_playing());
             }
         }
-        if egui_ctx.input_mut(|input| input.consume_shortcut(&Self::SHORTCUT_FULLSCREEN)) {
+        let mut fullscreen_pressed =
+            egui_ctx.input_mut(|input| input.consume_shortcut(&Self::SHORTCUT_FULLSCREEN));
+        if cfg!(windows) && !fullscreen_pressed {
+            // TODO We can remove this shortcut when we add some kind of preferences.
+            fullscreen_pressed = egui_ctx
+                .input_mut(|input| input.consume_shortcut(&Self::SHORTCUT_FULLSCREEN_WINDOWS));
+        }
+        if fullscreen_pressed {
             if let Some(player) = &mut player {
                 let is_fullscreen = player.is_fullscreen();
                 player.set_fullscreen(!is_fullscreen);