Email preview: fix sending preview if content in the editor is different from latest in the database

[simison]

Proposed changes:

• Fire auto-save before sending the email preview. Ensures the preview email has latest content from the post, instead of what might've been saved by editor previously.

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?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

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

Testing instructions:

• Create a post; good to test without saving it first as a draft, as well as saving it as a draft
• If you save a draft, go ahead and modify the text some more. Using numbers in content makes testing easy.
• Hit publish, hit "Send test email"
• Note auto-save kick on the background
• See that you get the email with latest content
• Without the change, latest unsaved changes aren't in the email

[github-actions]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WordPress.com Simple site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin, and enable the update/email-preview-save-draft branch.

• To test on Simple, run the following command on your sandbox:

  bin/jetpack-downloader test jetpack update/email-preview-save-draft
  

Interested in more tips and information?

• In your local development environment, use the jetpack rsync command to sync your changes to a WoA dev blog.
• Read more about our development workflow here: PCYsg-eg0-p2
• Figure out when your changes will be shipped to customers here: PCYsg-eg5-p2

[github-actions]

Thank you for your PR!

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• ✅ Add a "[Status]" label (In Progress, Needs Team Review, ...).
  
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Once your PR is ready for review, check one last time that all required checks appearing at the bottom of this PR are passing or skipped.
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• WordPress.com Simple releases happen daily.
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[lezama]

nice!

[simison]

@Automattic/jetpack-crew in case you had advice on how to handle Gutenberg functions and backwards compatibility with older WPs in Jetpack; this isn't really issue for .com since we run the latest.

Method introduced in WordPress/gutenberg#44971
It's here, and it's contents are stable so in theory I could just copy all that code here instead.

[anomiex]

Jetpack needs to support back to the version of the Gutenberg packages that is bundled in the previous WordPress release, which is currently 6.3.

I guess the case here is that 6.3 (and maybe 6.4 too?) doesn't have any version of the function at all, and you're wanting to copy-paste the implementation into Jetpack so the change you're making here still happens in 6.3? Be sure to include a comment indicating that the back-compat code can be removed when we drop support for the old version. Something along the lines of // @todo Remove the `if` check and `else` branch once WP 6.4 is the minimum supported version is fine, you don't have to get too fancy. Just be sure the comment clearly mentions an appropriate WordPress version so we can find it easily via a grep when we're making the PRs like #34210.

Or if it's ok that WP 6.3 just doesn't do whatever the new function does, that's fine with us too. Again though a comment mentioning the WP version when the if check can be removed would be useful.

[lezama]

Done!

[lezama]

like a charm

[anomiex]

Comment looks good to me now. Haven't reviewed the code itself, but someone else did earlier.