[PP-1] Add a normalizer for component tree items

Overview

Drupal core will soon add the ability to export content, which can be imported by recipes (see ✨ Add a command-line utility to export content in YAML format Active ). Its export is pluggable because it uses the core serialization system to normalize content for export.

Proposed resolution

XB should add a normalizer for component tree field items which ensure that XB pages -- or really, any entity using an XB field -- can be easily exported. Right now there are some issues; for example, the contrib Default Content module exports empty properties that fail validation on import, meaning that exporting an xb_page entity into your recipe involves a ton of very tedious editing for even minor changes.

User interface changes

None, this is simply integrating with a core API to help developers, recipe authors, and site template creators.