Data processors should not be created with the editing view document

[Reinmar]

Currently we do this in editors:

this.data.processor = new HtmlDataProcessor( this.editing.view.document );

Which makes no sense. Why passing the editing document to the data processor used in the data pipepline?

The problem is that DataController does not have its own document right now. It creates its document on the fly in toView(). This will need to be changed so DataController#constructor() exposes its #viewDocument. When creating a data processor you will do this:

this.data.processor = new HtmlDataProcessor( this.data.viewDocument );

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Note: Unfortunately, there will be no symmetry between the editing and data controllers. In the former, we keep only the view instance. In the latter, we won't have such an instance – we'll keep the view document directly in the controller. We discussed this with @scofalik and decided to go with this imperfect solution as we don't know yet if we'll ever need that view and what will be its shape (it's related to the performance optimization proposed by @scofalik to not recreate the entire view document on every editor.getData()).

[Reinmar]

Note: after this change, toView() should not create its fresh document.

[Reinmar]

Remember to update the tutorial about creating your own editor. I think the same code was used there.