Writer: allow custom Vue components for marks & nodes

I digged a bit and apparently you have to initialize NodeViews in the new EditorView() call. So it has to be an API extension in Core of some kind.

This would be really helpful for DreamForm.

@Tobias could you elaborate a bit on the use case? We’ve stayed away from actual components/blocks in ProseMirror as for that we have the blocks field instead. So there is an initial reistance in me to open up yet another (rather advanced and complicated) way that’s prone to many additional feature requests and issues plopping up. But that’s why some context and use cases would be great to understand the need a little more.

Currently, you have to use and understand Query language to write custom email templates in DreamForm. (Besides code of course)

Ideally, I want to add a content placeholder node that just offers a visual interface to select a field.

So, it’s an inline node, since it resolves to a string basically.