RestrictedEditing feature may produce multiple operations with the same base version

[ma2ciek]

While working on the #11634, I realized that a few tests break with the new API, mainly because the Document#version check has been moved to another place where versions are checked when they are added to the History instead of before being applied.

In #11634 (comment) I debugged the issue and came to these conclusions:

1. The addMarker() is called
2. The applyMarkerOperation() is called the first time and a new version for the operation is created
3. During the operation apply, but before it's done the RestrictedEditing detected that the marker has changed and is not flat (ensureNewMarkerIsFlat). As this is not a normal postfixer - model.markers.on( 'update:restrictedEditingException', ensureNewMarkerIsFlat( editor ) ); - the ensureNewMarkerIsFlat is called just after detecting the update of the marker.
4. The ensureNewMarkerIsFlat detects a marker that is not flat and updates it.
5. The udpateMarker() is called
6. The applyMarkerOperation() is called the second time and a new version for the operation is created - the same as during the 2. step.
7. The second operation is applied successfully and the document version is incremented.
8. The first operation can't be applied - the version of the operation is the same as the second one.