efl_input_focus: add event_flags

Summary:
It appears that it could be interesting to know if a focus event has
already been procecced or not. However, a focus event based on scrolling
activity is not possible, therefore, error about that.

ref T7652

Reviewers: cedric, zmike, stefan_schmidt

Reviewed By: zmike

Subscribers: reviewers, committers

Tags: efl

Maniphest Tasks: T7652

Differential Revision: https://phab.enlightenment.org/D7732