Forms: refactor Multiple and Single Choice fields

[monsieur-z]

Proposed changes:

#38916 made one of the Calyso e2e tests fail (see conversion linked below) because it changed the markup of the Multiple Choice and Single Choice blocks in the editor. It highlighted that the block and the inner block props were passed incorrectly. This PR refactors these two blocks to match how Gutenberg handles block and inner blocks (e.g. the List block). It should fix the failing e2e test as well.

In detail, the PR does the following:

• Move out the code for Multiple Choice and Single Choice out of child-blocks.js for readability, respectively in the jetpack-field-multiple-choice and jetpack-field-single-choice folders
• Extract the code shared by these two fields in jetpack-field-choice
• Updated some selectors in editor.scss to prevent any design breakage
• Extract getFieldLabel in a separate file
• Create the mergeSettings utility to merge a block settings with default settings
• Deleted the now unused jetpack-field-option.js file

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

Conversation: p1724766845302749-slack-C01U2KGS2PQ

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

No.

Testing instructions:

• Spin up a test site with the trunk branch. You need to be able to switch branch later on.
• Create a new post
• Add a Multiple Choice field from the block inserter (it will be wrapped in a form)

• Add a Single Choice field to the form

• Save the draft and open the preview in a new tab
• In a new tab, update the Jetpack version so it uses this branch
• Visit the post you've created. You should not see any errors in the UI or the console.
• Verify the blocks work like they do on trunk
• Open the preview and make sure the form works as expected

Note: the label is different in the editor and the preview as long as it's not edited. This issue is already present on trunk and will be addressed in a separate PR.

[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 refactor/form-choice-fields branch.

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

  bin/jetpack-downloader test jetpack refactor/form-choice-fields
  

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:

• ✅ Include a description of your PR changes.
  
• ✅ Add a "[Status]" label (In Progress, Needs Team Review, ...).
  
• ✅ Add testing instructions.
  
• ✅ Specify whether this PR includes any changes to data or privacy.
  
• ✅ Add changelog entries to affected projects
  

This comment will be updated as you work on your PR and make changes. If you think that some of those checks are not needed for your PR, please explain why you think so. Thanks for cooperation 🤖

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The e2e test report can be found here. Please note that it can take a few minutes after the e2e tests checks are complete for the report to be available.

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Follow this PR Review Process:

1. Ensure all required checks appearing at the bottom of this PR are passing.
2. Choose a review path based on your changes:
   • A. Team Review: add the "[Status] Needs Team Review" label
     • For most changes, including minor cross-team impacts.
     • Example: Updating a team-specific component or a small change to a shared library.
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   • C. Both: Start with Team, then request Crew
     • For complex changes or when you need extra confidence.
     • Example: Refactor affecting multiple systems.
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[coder-karen]

Nice work on this!
Tests well.