Migrate Core Data schema, models, and manager to dedicated WordPressData module.

[mokagio]

Just an issue to collect the various PRs involved in this non-trivial task.

Internal refs:

• pbArwn-7b1-p2
• pbArwn-78x-p2

[dangermattic]

Thanks for reporting! 👍

[mokagio]

#24153

[mokagio]

#24164

[mokagio]

#24157