Improved focus management test.

[oskarwrobel]

Suggested merge commit message (convention)

Fix: Improved focus management test. Closes ckeditor/ckeditor5#4779.

---

Needs: ckeditor/ckeditor5-ui#194

[oleq]

The editor toolbar remains now, but the focus does not go into the URL input:

[oskarwrobel]

1. Bug is already on master.

2. It's really easy to fix it:

this._balloon.add( {
	view: this.formView,
	position: this._getBalloonPositionData()
} );

if ( focusInput ) {
	this.formView.urlInputView.select();
}

vs

this._balloon.add( {
	view: this.formView,
	position: this._getBalloonPositionData()
} ).then( () => {
	if ( focusInput ) {
		this.formView.urlInputView.select();
	}
} );

3. There is a problem (related to: https://github.com/ckeditor/ckeditor5-ui/issues/203) with unit tests. Test finishes before promise.then() is called.

[oskarwrobel]

It's an ugly hack, I don't like it but I didn't figure out anything less complicated.

[oskarwrobel]

I'm refactoring Link tests so let's wait with review till I finish.