Blogging prompts: move to experimental blocks

[creativecoder]

Follow up to #26680

Changes proposed in this Pull Request:

• Moves the blogging prompt editor extension to experimental, to make it available on WP.com sites
• Slightly refactors jetpack_get_daily_blogging_prompts since a timestamp can now be specified

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?

Jetpack product discussion

See #26680

Does this pull request change what data or activity we track or use?

No.

Testing instructions:

• Be sure the site is connected to WP.com to load Jetpack blocks in the editor
• Enable beta blocks by adding define( 'JETPACK_EXPERMINENTAL_BLOCKS', true ) (or Settings > Jetpack Constants if you're using jurassic.ninja)
• Set the site as "having a blog" by doing at least one of the following
  • Set the site_intent option to write
  • Set the front page to show posts in Settings > Reading
  • Set a static page for the posts page in Settings > Reading
• Create a new post, you should see a writing prompt in the placeholder for the first paragraph
• Create a new post and add the answer_prompt query param with the prompt id for today as the value (e.g. /wp-admin/post-new.php?answer_prompt=2129), and you should see a writing prompt as a pullquote block, the tag dailyprompt added to the post, and the _jetpack_blogging_prompt_key post meta set to the prompt id.
• Create a new page or custom post type, and you should not see the writing prompt
• Open an existing post, and you should not see the writing prompt

[github-actions]

Are you an Automattician? You can now test your Pull Request on WordPress.com. On your sandbox, run bin/jetpack-downloader test jetpack update/blogging-prompts-experimental to get started. More details: p9dueE-5Nn-p2

[github-actions]

Thank you for your PR!

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Jetpack plugin:

• Next scheduled release: December 6, 2022.
• Scheduled code freeze: November 28, 2022.

[roo2]

Tested on jurassic.tube, LGTM. Just need to change the base back to trunk

The base branch was changed.

[roo2]

oops, sorry, why did I think #26680 was merged already 😅 . So after that's merged, then this will need to have base changed to trunk 😛.

[coder-karen]

LGTM.