efl_ui_tab_pager: do not directly inherit from spotlight anymore
spotlight moved away from layout, this could have also been solved with
setting a edje object as resize object. However, this commit now
contains the spotlight internally.
The resons why containing it internally is better:
- You now only have one way of selecting a page, marking it as selection
via the selectable API
- You cannot build race conditions between selecting a page and setting
the active_element anymore
- The tab_pager is now also just a simple single_selectable implementor,
which makes this whole usage more convinient.
- There is now a event you can listen to if you want to know if
something has changed the selected item
- push and pop would have never worked correctly in the tab_pager, as
the item would have appeared always before the item was "faded" in. This
possibility is not given anymore
Last but not least, this makes tab_pager usable again, the tab bar is
displayed again.
Differential Revision: https://phab.enlightenment.org/D10775