model.Differ does misses some cases for attribute changes transformations

[scofalik]

Well, the thing is simple: right now we are handling just one out of four possible cases for attribute changes. We need to handle all four "intersecting" scenarios:

{   [   }   ]    -->    {   }[      ]
{   [   ]   }    -->    {           }
[   {   }   ]    -->    [           ]
[   {   ]   }    -->    [      ]{   }

Where {} is incoming change and [] is already buffered chage.

[scofalik]

Actually, after further research, I realized that there are only three possible scenarios:

1. Incoming change is same as buffered change.
2. Incoming change contains buffered change.
3. Incoming change is inside buffered change.

AFAICS, there will never be intersecting scenarios because model.Differ iterates over item in the model tree:

for ( const item of operation.range.getItems() ) {
	if ( this._isInInsertedElement( item.parent ) ) {
		continue;
	}

	this._markAttribute( item );
}

So there never will be a situation with intersecting attribute change items.