Forms: add help for form blocks vs synced forms

[edanzer]

Proposed changes:

This is a trial PR. It offers a simple way to address confusion for users when we launch Centralized Form Management, and they do not see their forms in the central forms list because we only show form posts not form blocks.

We add a "Missing Forms?" button when the forms list is empty, and a similar link in the page subititle. Both open a modal with an explanation.

Screenshots

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:

Enable these feature flags:

add_filter( 'jetpack_forms_alpha', '__return_true', 20 );
add_filter( 'jetpack_block_editor_feature_flags', 'eb_register_feature' );
function eb_register_feature( $flags ) {
    $flags['central-form-management'] = true;
    return $flags;
}

Test:

• Go to Jetpack > Forms, and be sure you are on the Forms tab
• Confirm the Missing Forms? link in the subtitle appears and opens the modal
• Move all forms in your forms list to trash, and confirm the Missing Forms? button shows and opens the modal.

[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 WoA dev 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 (Jetpack), and enable the add/forms-wpbuild-dashboard-block-clarification branch.
• To test on Simple, run the following command on your sandbox:

bin/jetpack-downloader test jetpack add/forms-wpbuild-dashboard-block-clarification

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!

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

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---

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[jp-launch-control]

Code Coverage Summary

Coverage changed in 1 file.

File	Coverage	Δ%	Δ Uncovered
projects/packages/forms/src/dashboard/wp-build/hooks/use-page-header-details.tsx	0/37 (0.00%)	0.00%	3 ❤️‍🩹

1 file is newly checked for coverage.

File	Coverage
projects/packages/forms/src/dashboard/wp-build/components/forms-help-modal/index.tsx	0/3 (0.00%) 💔

Full summary · PHP report · JS report

_{If appropriate, add one of these labels to override the failing coverage check: Covered by non-unit tests Use to ignore the Code coverage requirement check when E2Es or other non-unit tests cover the code Coverage tests to be added later Use to ignore the Code coverage requirement check when tests will be added in a follow-up PR I don't care about code coverage for this PR Use this label to ignore the check for insufficient code coveage.}