Conversion builder refactoring

[pjasiun]

There are 2 problems with the current conversion builder.

First, since the API is chainable, not declarative, it is hard to pass parameters to the config. Recently we realized that we need to make plugins like font size or headings configurable and conversion builder is nothing similar to what you want to pass to the config.

Second, since conversion builder mix all converters together it is hard to learn, based on in, how to create your custom converter.

This is why converters should be more specific. In the F2F talk with @Reinmar and @scofalik we agreed on the solution simmilar to what @szymonkups proposed some time ago.

editor.conversion.for( 'model' ).add( elementToElement( 'paragraph', 'p' ) )

There will be specific model to view converters like:

elementToElement
attributeToElement
attributeToAttribute
markerToElement
markerToHighlight

And corresponding view to model converters.

editor.conversion will have predefined sets of dispatchers:

editor.conversion = new Conversion();
editor.conversion.register( 'data', editor.data.moveToView );
editor.conversion.register( 'editing', editor.editing.moveToView );
editor.conversion.register( 'model', [ editor.editing.moveToView, editor.data.moveToView ] );
editor.conversion.register( 'view', editor.data.viewToModel );
// The type of the conversion might be taken based on the constructor type.

Conversion function should get configuration defined the way it will be simple to use it with the conversion definition.