edje_calc: replace eina_stringshare_ref with eina_stringshare_add

Summary:
When there is circular dependency in edc, a bunch of CRI log is printed.
This patch fixes it.
```
ERR<10159>:edje lib/edje/edje_calc.c:3919 _edje_part_recalc() Circular dependency in the group 'test' : longpartname -> longpartname -> longpartname2
ERR<10159>:edje lib/edje/edje_calc.c:3896 _edje_part_recalc() Circular dependency when calculating part "longpartname". Already calculating XY [03] axes. Need to calculate Y [02] axes
CRI<10159>: lib/eina/eina_share_common.c:559 _eina_share_common_node_from_str() *** Eina Magic Check Failed at 0x7fb7c93ebf60 !!!
    Input handle is wrong type.
    Expected: 98761254 - Eina Stringshare Node
    Supplied: 2f736e6f - (unknown)

CRI<10159>: lib/eina/eina_share_common.c:559 _eina_share_common_node_from_str() *** Eina Magic Check Failed at 0x7fb7c93ec5d1 !!!
    Input handle is wrong type.
    Expected: 98761254 - Eina Stringshare Node
    Supplied: 5f747261 - (unknown)
```
If string is already stored, `eina_stringshare_add` increase its reference count.

Test Plan:
test.c
```
//edje_cc test.edc && gcc -o test test.c `pkg-config --libs --cflags elementary`

int main(int argc, char **argv)
{
   elm_init(argc, argv);

   Evas_Object *win = elm_win_util_standard_add("test", "test");

   Evas_Object *layout = elm_layout_add(win);
   elm_layout_file_set(layout, "./test.edj", "test");
   elm_win_resize_object_add(win, layout);
   evas_object_show(layout);
   evas_object_resize(win, 200, 200);
   evas_object_show(win);

   elm_run();

   elm_shutdown();

   return 0;
}
```

test.edc
```
collections {
   group { name: "test";
      parts {
         rect { name: "longpartname";
            desc { "default";
                rel1.to: "longpartname2";
            }
         }
         rect { name: "longpartname2";
            type: RECT;
            desc { "default";
                rel2.to: "longpartname";
            }
         }
      }
   }
}
```

Reviewers: SanghyeonLee, zmike

Reviewed By: SanghyeonLee

Subscribers: cedric, #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D8717