refactor(API): don't expose private symbols in lvgl.h. phase-out "_lv*" names (#6068)

Co-authored-by: Gabor Kiss-Vamosi <kisvegabor@gmail.com>

examples/others/snapshot/lv_example_snapshot_1.c

@@ -13,7 +13,7 @@ static void event_cb(lv_event_t * e)
         }
 
         /*Update the snapshot, we know parent of object is the container.*/
-        snapshot = lv_snapshot_take(img->parent, LV_COLOR_FORMAT_ARGB8888);
+        snapshot = lv_snapshot_take(lv_obj_get_parent(img), LV_COLOR_FORMAT_ARGB8888);
         if(snapshot == NULL)
             return;
         lv_image_set_src(snapshot_obj, snapshot);