Make model/Writer and view/DowncastWriter more consistent

[f1ames]

Follow up of #4409:

The only thing which makes me sad about this change is that after it the DowncastWriter.rename() method signature will be inconsistent with the model/writer.rename() method signature. (...) it may bring some confusion for developers who use both model and view writers frequently.

So the purpose of this ticket is to make model/Writer#rename() and view/DowncastWriter#rename() methods signature consistent by changing model/Writer#rename() parameters order.

[Reinmar]

A more specific issue regarding the insertion methods: https://github.com/ckeditor/ckeditor5-engine/issues/1724.

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