Forms: Add ability output schemas

[DevinWalker]

Fixes #

This PR is open because Forms is already the strongest Jetpack Abilities API integration, and agents need dependable response shapes to use it safely. It keeps the change limited to output contracts and a small no-op guard so the broader rollout can stay reviewable.

Proposed changes

• Add explicit output schemas for the Jetpack Forms abilities so agent clients can reason about response shapes.
• Tighten jetpack-forms/update-response so calls must include a mutation field, matching the declared object output contract.
• Return the admin edit URL from jetpack-forms/get-form instead of the public permalink.
• Strengthen Forms ability tests for public metadata, output schemas, no-op update handling, and edit URL behavior.

Related product discussion/links

• JETPACK-1769: https://linear.app/a8c/issue/JETPACK-1769/track-targeted-jetpack-abilities-api-rollout-prs

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

No.

Testing instructions

• From projects/packages/forms, run:
  • php vendor/bin/phpunit-select-config phpunit.#.xml.dist --colors=always tests/php/abilities/Forms_Abilities_Test.php
• Confirm the test passes with 30 tests, 227 assertions.
• Optional broader check: CI=true jp test php packages/forms -v currently reaches PHPUnit but fails in existing webhook localhost tests unrelated to these Forms abilities changes.

[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 codex/forms-abilities-output-schemas branch.
• To test on Simple, run the following command on your sandbox:

bin/jetpack-downloader test jetpack codex/forms-abilities-output-schemas

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• 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!

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Code Coverage Summary

Coverage changed in 1 file.

File	Coverage	Δ%	Δ Uncovered
projects/packages/forms/src/abilities/class-forms-abilities.php	600/651 (92.17%)	1.56%	0 💚

Full summary · PHP report · JS report

[DevinWalker]

Superseded by #49954 after renaming the source branch from codex/forms-abilities-output-schemas to add/forms-abilities-output-schemas.