Efl.Ui.Slider: add default indicator format to %0.2f

This was broken in legacy code as well.
Thanks to @taxi2se for reporting.

elm_test -> slider -> check vertical slider

@fix

src/lib/elementary/efl_ui_slider.c

@@ -1146,6 +1146,8 @@ _efl_ui_slider_efl_canvas_group_group_add(Eo *obj, Efl_Ui_Slider_Data *priv)
    _elm_access_callback_set
      (_elm_access_info_get(obj), ELM_ACCESS_STATE, _access_state_cb, NULL);
 
+   efl_ui_format_string_set(efl_part(obj, "indicator"), "%0.2f");
+
    evas_object_smart_changed(obj);
 }