Forms: Fix empty form block - show nothing

[enejb]

Fixes #41244

This PR fixes the case where a user added the contact form block but didn't select any form.

Editor

Front end Before: We should show a simple contact form. Notice that the form doesn't have the expected styling.

Front end | After: We show nothing.

Proposed changes:

• Remove the form from the fronted if the user doesn't select the a type of form.

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?

No

Testing instructions:

• Load this PR.
• Create a new page and add the form block. Publish the post.
• Notice that on the front end we don't show any type of form.

[github-actions]

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[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 fix/empty-form-block-remove-render branch.

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  bin/jetpack-downloader test jetpack fix/empty-form-block-remove-render
  

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[simison]

How's the backwards compatibility for something like this?