[meta] Tasks to remove the Claro theme

Problem/Motivation

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

The removal of Claro was approved in #3576460: [policy, no patch] Deprecate and remove Claro.

Remaining tasks

1. ✅Create a child issue to remove the core extension. #3584639: Remove the Claro theme
2. ✅Deprecate the extension in the current minor development branch. If the next major branch is open, the extension can be removed via a separate patch (to avoid dependent patches), otherwise an issue should be opened to remove the extension once the next major branch is open.
3. ✅Manually test upgrading from the core extension to the contrib extension. #3586197: Test the upgrade path for Claro theme
4. ✅Triage core issues for Claro in the core queue and move either to the contrib project or the relevant core component. Restore the status to what it was before it was postponed. Also, is the issue moved to contrib, then move any change record.
5. ✅Move all core documentation for Claro to the contrib project. Make issues in the contrib project to update or add links to the documentation on the project page.

Release notes snippet