Social Preview: add to pre-publish sidebar

[ramonjd]

Fixes #19915

Changes proposed in this Pull Request:

This PR adds the Jetpack Social Preview panel to the pre-publish sidebar.

The Social Preview panel still appears in the Jetpack sidebar. (Or should we remove it from here?)

Jetpack product discussion

p1HpG7-c4u-p2

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

Nah.

Testing instructions

1. Run locally and create a new post.
2. Check that the social preview appears (and the preview modal works) in the Jetpack menu, and in the pre-publish sidebar.
3. Apply D62094-code to your sandbox, and check that the panel displays the upgrade nudge for a free, sandboxed site.
4. Upgrade your test site to a Business plan. The Social Preview panel should show the preview modal.

[matticbot]

Caution: This PR has changes that must be merged to WordPress.com
Hello ramonjd! These changes need to be synced to WordPress.com - If you 're an a11n, please commandeer and confirm D62094-code works as expected before merging this PR. Once this PR is merged, please commit the changes to WP.com. Thank you!
This revision will be updated with each commit to this PR

[github-actions]

Thank you for your PR!

When contributing to Jetpack, we have a few suggestions that can help us test and review your patch:

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Jetpack plugin:

• Next scheduled release: July 6, 2021.
• Scheduled code freeze: June 28, 2021.

[andrewserong]

This is working nicely for me, a good simple addition! LGTM

The Social Preview panel still appears in the Jetpack sidebar. (Or should we remove it from here?)

Personally, I like that it appears in multiple places. After the post or page is published, I might want to go back in and check what the preview looks like before I share a link on Twitter. And if I already know it's a Jetpack feature, then being able to find it from the Jetpack plugin menu as well is nice.

✅ Tested that it works correctly in my local development environment
✅ In wpcom, on a free plan site, and a personal plan site, the social preview button opens up the modal with the upgrade nudge
✅ In wpcom on a business plan site, the social preview behaviour works correctly in the pre publish panel and within the Jetpack plugin menu

[andrewserong]

Oh, and it looks like the failing CI jobs might be due to rate limiting? 🤞 they'll be resolved by re-running them at some stage?

[kraftbj]

I'm okay with it being in both places, or at least removing it from the Jetpack panel later under a separate discussion.

[github-actions]

Great news! One last step: head over to your WordPress.com diff, D62094-code, and commit it.
Once you've done so, come back to this PR and add a comment with your changeset ID.

Thank you!

[ramonjd]

r226584-wpcom