[Meta] Tasks to deprecate Seven

Problem/Motivation

This issue is to coordinate and track the steps needed to deprecate Seven. See Remove a core theme and move it to a contributed project of the deprecation policy.

The deprecation of Seven was approved in TBD.

Steps to reproduce

Proposed resolution

1. Change installer to use Claro: #3085219: Installer is not very usable in Claro.
2. Convert integrations.
   • Remove usages of Seven from tests: #3302800: Core tests need to filter out deprecated themes when looping over all themes
   • Remove theme from profiles. #3277057: Make Claro the default admin theme in Standard profile
   • #3304655: Umami depends on Seven
   • Remove from update path tests
     • Remove the templates from themes that are staying in core, leave them in deprecated themes
     • Keep skipping the template in the stable copies test.
3. Create the contrib project, Seven, with a stable release. See the deprecation policy for the git commands.
4. Deprecate the core Seven theme, #3084814: Deprecate Seven theme
   1. Create a section on Deprecated and obsolete themes and themes to provide recommendations for sites using theme Seven. The recommendation are to include instructions for sites using Seven and for contributed themes that depend on Seven.
   2. Set lifecycle to deprecated.
   3. Set lifecylcle_link to the section added above, https://www.drupal.org/node//3223395#s-Seven.
   4. The change record for this issue includes a link to the doc page.

User interface changes

API changes

Data model changes

Release notes snippet