[atspi] keep eo_obj as current highlighted object for widget item

[atspi] keep eo_obj as current highlighted object for widget item
So far, elm_object_accessibility_highlight_set have used VIEW object of Elm_Object_Item.
But, we cannot get Elm_Object_Item related data from VIEW which is returned by _elm_object_accessibility_currently_highlighted_get
We need to use currently highlighted object with some APIs such as elm_interface_atspi_accessible_state_changed_signal_emit.
But, we cannot use this kind of API with VIEW object.

Change-Id: I85ee98c4e2510c8e59c7fd0758281dfa9282f12e