chore(color): improvements for Lua LVGL API (#6676)

Co-authored-by: philmoz <phil.a.mitchell@gmail.com>

radio/src/gui/colorlcd/libui/window.cpp

@@ -405,6 +405,11 @@ void Window::show(bool visible)
   }
 }
 
+bool Window::isVisible()
+{
+  return !_deleted && lvobj && !lv_obj_has_flag(lvobj, LV_OBJ_FLAG_HIDDEN);
+}
+
 void Window::enable(bool enabled)
 {
   if (!_deleted && lvobj) {

radio/src/gui/colorlcd/libui/window.h

@@ -185,6 +185,7 @@ class Window
 
   virtual void show(bool visible = true);
   void hide() { show(false); }
+  bool isVisible();
   virtual void enable(bool enabled = true);
   void disable() { enable(false); }