Problem/Motivation
In #3366083: [META] Hooks via attributes on service methods (hux style) we proposed to provide a new way to implement hooks, using object methods with attributes.
A similar system already exists in contrib: https://drupal.org/project/hux
In this issue we will do proof-of-concept implementation and experiments.
Once this is done, we can split out real implementation issues that can then be developed and merged one by one.
E.g. perhaps there will be separate refactoring issues as preparation for the new system.