[Meta] Tasks to deprecate Book module

Problem/Motivation

Track the steps needed to remove extension Book from core to contrib. See Remove a core module and move it to a contributed project of the deprecation policy.

The contrib project is ?

The removal of extension Book was approved in #3265493: [Policy] Move book to contrib in Drupal 11.

Remaining tasks

1. Begin finding someone to maintain the contrib version of the Book module.
2. Move integrations implemented by other modules to the Book module.
   Create child issues or child meta issues, as needed, to address the following points. Not all points will apply to all extensions.
   • Move non-migration tests to the Book module. #3376271: Move non-migration book-related tests to the Book module
   • Move Help Topics to the Book module. #3376261: Move help topics to book module
   • Remove use of book in non profile and update tests. #3376369: Remove use of book in non profile and update tests
   • Use of book in tests #3414637: Remove usages of book module from tests
   • Remove the Book module from one or more profiles. #3410220: Remove book module from all core themes
   • Remove templates from the Book module’s markup.
     • Remove templates from themes that are staying in core, leave them in deprecated themes #3410216: Remove book module from themes
     • Keep skipping the template in the stable copies test.
   • For a module, handle migrations, if the module has migrations.
     • Move migration tests to the module. #3376259: Move book migrations tests to book module
     • #3376262: Remove install of book module from migration tests outside of the module
3. Do a thorough search of core for any remaining references to the Book module. If references are found, outside of the Book module, then create issues to remove the references.
4. Create the contrib project with a stable release. Follow the process in Create the contrib project with a stable release for creating the sub tree split.
5. Deprecate the core extension. #3413932: Deprecate Book module