efl_io_model: start early on monitoring

efl_io_model: start early on monitoring

Summary:
Little introduction into what eio did before this commit:
Efl.Io.Model creation:
  - direct ls of a directory in a thread (A)
  - take all the contents of a directory and feed it slowly back into
the mainloop
  - when all events have been feeded back to the mainloop and have been
processed: start monitoring (B)

However, any file created between (A) and (B) will not be in the model,
since not the listing nor the monitoring did caputure it. Hence we need
to start monitoring before we actaully start listing. In the callbacks
we then check if we already published something.

ref T7311

Reviewers: zmike, cedric

Reviewed By: cedric

Subscribers: cedric, #reviewers, #committers

Tags: #efl

Maniphest Tasks: T7311

Differential Revision: https://phab.enlightenment.org/D8525