Forms: Add multi step forms

[lezama]

This pull request introduces multistep capabilities to the Jetpack forms package, allowing users to divide forms into multiple steps. This feature enhances the user experience for complex forms by breaking them into manageable chunks.

See: #41080

Proposed changes:

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:

• Go to '..'

[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-multistep branch.
• To test on Simple, run the following command on your sandbox:

bin/jetpack-downloader test jetpack add/forms-multistep

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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• ✅ 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 🤖

---

Follow this PR Review Process:

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Jetpack plugin:

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[jp-launch-control]

Code Coverage Summary

Coverage changed in 10 files. Only the first 5 are listed here.

File	Coverage	Δ%	Δ Uncovered
projects/packages/forms/src/blocks/contact-form/edit.js	0/138 (0.00%)	0.00%	99 💔
projects/packages/forms/src/contact-form/class-contact-form-plugin.php	294/953 (30.85%)	-2.18%	71 💔
projects/packages/forms/src/contact-form/js/validate-helper.js	16/54 (29.63%)	-70.37%	38 💔
projects/packages/forms/src/contact-form/class-contact-form.php	558/885 (63.05%)	-2.10%	29 💔
projects/packages/forms/src/blocks/contact-form/child-blocks.js	0/97 (0.00%)	0.00%	26 💔

24 files are newly checked for coverage. Only the first 5 are listed here.

File	Coverage
projects/packages/forms/src/blocks/contact-form/components/add-step-controls/index.js	0/26 (0.00%) 💔
projects/packages/forms/src/blocks/contact-form/components/icons/StepContainerIcon.js	0/1 (0.00%) 💔
projects/packages/forms/src/blocks/contact-form/components/icons/StepIcon.js	0/1 (0.00%) 💔
projects/packages/forms/src/blocks/contact-form/components/step-controls/index.js	0/23 (0.00%) 💔
projects/packages/forms/src/blocks/form-progress-indicator/edit.js	0/14 (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.}

[simison]

Spaces instead of tabs here.