feat(obj) add lv_obj_move_to_index(obj, index), renamed lv_obj_get_child_id(obj) to lv_obj_get_index(obj) (#2514)

* - renamed lv_obj_get_id(obj) to lv_obj_get_index(obj).

- added lv_obj_move_to_index(obj, index).

* automatic review comment fixed

* removed unused variable

* review issue

* restored deprecated function in header, otherwise Build Micropython with LVGL submodule / build (pull_request)  failes

* moved deprecated lv_obj_get_child_id() back to lv_obj_tree.h, otherwise Micropython will not build

* inline function did not work

* made deprecated function 'static inline'

* and now also inline

* move static inline function to lv_api_map.h again

* removed lv_obj_move_up/down

* changed log to warning for deprecated function

* redefined lv_obj_move_foreground(obj) and lv_obj_move_background(obj) as inline functions now calling lv_obj_move_to_index(obj, index).

- lv_obj_swap(obj1, obj2) added. (#2461)

docs/overview/layer.md

@@ -42,7 +42,7 @@ lv_obj_del(label2);
 
 There are 4 explicit way to bring an object to the foreground:
 - Use `lv_obj_move_foreground(obj)` to explicitly tell the library to bring an object to the foreground. Similarly, use `lv_obj_move_background(obj)` to move to the background.
-- Use `lv_obj_move_up(obj)` moves the object one position up in the hierarchy, Similarly, use `lv_obj_move_down(obj)` moves the object one position down in the hierarchy. 
+- Use `lv_obj_move_to_index(obj, index)` to set the index of the object in its parent. 
 - Use `lv_obj_swap(obj1, obj2)` to swap the relative position of two objects.
 - When `lv_obj_set_parent(obj, new_parent)` is used, `obj` will be on the foreground on the `new_parent`.