Summary:
It is a mixin only because of the setter method for the "closed" property,
otherwise, it would be a pure interface.
Nobody is setting that property, so let's just remove the setter (leaving only
the getter) and make this class an interface.
This should clear the scenario for languages currently having issues with
mixins (like C#).
Related to T7601.
Test Plan: Nothing changes. Make check and examples still work.
Reviewers: zmike, bu5hm4n, cedric
Reviewed By: cedric
Subscribers: cedric, #reviewers, #committers
Tags: #efl
Differential Revision: https://phab.enlightenment.org/D7570
1534f50be0