Update model selection data before the post fixers are called.

[oskarwrobel]

Suggested merge commit message (convention)

Fix: Update model selection data after each change that affects the selection. Closes https://github.com/ckeditor/ckeditor5-engine/issues/1673.

---

Additional information

For example – encountered issues, assumptions you had to make, other affected tickets, etc.

[coveralls]

Coverage increased (+7.0e-06%) to 99.992% when pulling 082847c on t/1673 into 5862d70 on master.

[pjasiun]

I think that we should keep selection attributes and markers up-to-date, so it should be updated after each operation applied.