[meta] Tasks to deprecate the Telephone module

Problem/Motivation

Track the steps needed to deprecate extension Telephone. See Remove a core extension and move it to a contributed project of the deprecation policy.

The removal of extension Telephone was approved in #3266465: [policy, no patch] Remove Telephone module from core.

Remaining tasks

1. Begin finding someone to maintain the contrib version of the extension. smustgrave has volunteered
2. Add the extension to the list of the Upcoming Deprecations. - Done
3. Move integrations implemented by other modules to the extension.
   Create child issues or child meta issues, as needed, to address the following points. Not all points will apply to all extensions.
   • Move tests to the extension #3594057: Remove/replace any tests using telephone
   • Move Help Topics to the extension. #3594241: Remove reference of telephone from help topics
   • Remove references to the extension from database dumps. - Not used in any DB dumps
   • Remove templates from the extension’s markup.
     • Remove templates from themes that are staying in core, leave them in deprecated themes There are none :)
     • Keep skipping the template in the stable copies test.
4. Do a thorough search of core for any remaining references to the extension. If references are found, outside of the extension, then create issues to remove the references.
5. Create the contrib project with a stable release, before the alpha version of the major release. Follow the process in Create the contrib project with a stable release for creating the sub tree split.
6. Deprecate the core extension. #3594202: Deprecate the Telephone module - in review
7. Create an issue, 'Ensure that Telephone does not get special core treatment' in the packages.drupal.org issue queue to ensure that the composer namespace for the contributed project matches the core one after removal. This is to allocate the drupal/telephone Composer namespace to contrib extension rather than the core extension. - Opened https://git.drupalcode.org/project/project_composer/-/work_items/3583681
8. Update the Deprecated and obsolete extensions