This adds a data transform plugin system to Paragraphs Sets by wrapping that module's data_alter hooks.

The annotated plugins operate kinda sorta like migration process plugins. Currently include plugins:

- `simple`: an identity plugin
- `create_entity`: construct nested entities for an entity reference field

For example, in a paragraphs set, we want a paragraph that references custom entities to prepopulate (i.e., create) the entities: