Likes: display like count in post list table, when Likes module is enabled

This is a follow-up to #19659.

### Steps to reproduce

1. Start with a site using a block-based theme like Twenty Twenty Four
2. Activate the Jetpack plugin
3. Connect your site to your WordPress.com account
4. Go to Appearance > Editor
5. Insert a Like block somewhere in your single posts template.
6. You'll now be able to Like your posts.
7. Go to Posts > All Posts
* You will not see any indication that you've received Likes there.
8. Now go to Jetpack > Settings > Sharing
9. Enable the Likes module
10. Go back to Posts > All Posts
* You will now see the Likes count

Ideally, when the Like block is used somewhere in the active theme's templates, we should add the column to the post list table, vs. just doing it when the module is active:
https://github.com/Automattic/jetpack/blob/8e9db5858a34c1d29e0e40508d71f7a3c4a0ed3c/projects/plugins/jetpack/modules/likes.php#L245-L248

Start with the likes.php section linked in the issue and review the prior discussion in #19659. Trace how the post list table column is currently added and how active block-based templates can be inspected. Done means the Likes count column appears when the Like block is used in the active templates, without requiring the Likes module to be enabled.

Written by the indexing model from the issue text.