app: support changing Window options at runtime

A Window can now be requested to change its options after
it has been started via its Option method.

All options are supported on macOS, Windows and X11.
On Wayland, only the Size and Title options can be changed
at runtime.

Signed-off-by: pierre <pierre.curto@gmail.com>

app/internal/wm/os_macos.go

@@ -172,11 +172,10 @@ func (w *window) Option(opts *Options) {
 func (w *window) SetWindowMode(mode WindowMode) {
 	switch mode {
 	case w.mode:
-		return
-	case Fullscreen:
+	case Windowed, Fullscreen:
 		C.gio_toggleFullScreen(w.window)
+		w.mode = mode
 	}
-	w.mode = mode
 }
 
 func (w *window) SetCursor(name pointer.CursorName) {