edje_edit: add API for get part item attributes by item index

edje_edit: add API for get part item attributes by item index

Cedric revert patch 6f7608befd006f8076d237bee5d17c9e9e1e09ac same days
ago.

<quote Cedric>
Your patch 6f7608befd006f8076d237bee5d17c9e9e1e09ac did break elemines
which does relly on the proper index to be given to it. I think
Edje_Edit should be fine and use the index if no name is provided (See
edje_load.c around L1180). In all case this was clearly an ABI break and
needed to be reverted.
</quote Cedric>

So now edje_cc not guarantee name for part items. This is bad, because
edje_edit use item name for access to item attributes. If item have not
name we cann't get it attributes, because edje_edit compare the given
name with part items name from edj-file, strcmp dislake NULL args.
For now I see one way mark all edje_edit_part_item* APIs as deprecated
and add new APIs for manage part items by index.

For clearly and history:
The eason for revert - https://phab.enlightenment.org/D3820
The proposed solution - https://phab.enlightenment.org/D3907

Change-Id: I1d2d497749bdf40fd2ed05deaf488d8dd5e533fe