introduce isBlock and isInline queries

[ianstormtaylor]

Do you want to request a feature or report a bug?

Improvement / debt.

What's the current behavior?

Right now blocks and inlines are defined at the data level, with object: 'block' or object: 'inline'. But based on #2757 this restriction is in question.

What's the expected behavior?

Instead, we can use the same pattern for isVoid and isAtomic. Specifically that schemas can define an isInline: true property for nodes (defaulting to false since blocks are much more common). As well as editor.isInline(node) and editor.isBlock(node) queries.

The block/inline property of nodes would then be controlled at the editor level, and could be changed like in CSS. It no longer needs to be hardcoded in the data model.

[ianstormtaylor]

Fixed by #3093.