Forms: Update "Action after submit" sidebar section

[dhasilva]

Part of FORMS-246
Follow-up to #45273 and #45487

Proposed changes:

This adds two new attributes, disableSummary and confirmationType, deprecating customThankyou without requiring a formal block deprecation. This allows for a custom message to also include the summary and simplifies the UX.
See screenshots at the bottom of the description.

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?
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Jetpack product discussion

p1760435815738269/1759925173.540499-slack-C052XEUUBL4

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

Testing instructions:

• Submit existing blocks without changing them
• Check that the post-submission screen works as expected, same as before
• Edit an existing form, check that the "Action after submit" section matches the old behavior
• Save and submit. Check that the post-submission screen works as expected
• Create a new form and set the confirmation type settings.
• Publish and submit. Check that the post-submission screen works as expected
• Test with different settings combinations, like redirections or text with or without custom messages and summary

Before	After

[github-actions]

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bin/jetpack-downloader test jetpack update/forms-action-after-submit

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[github-actions]

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[jp-launch-control]

Code Coverage Summary

Coverage changed in 2 files.

File	Coverage	Δ%	Δ Uncovered
projects/packages/forms/src/blocks/contact-form/edit.tsx	0/269 (0.00%)	0.00%	9 💔
projects/packages/forms/src/contact-form/class-contact-form.php	624/1157 (53.93%)	0.42%	4 💔

Full summary · PHP report · JS report

_{Coverage check overridden by Coverage tests to be added later Use to ignore the Code coverage requirement check when tests will be added in a follow-up PR .}

[CGastrell]

Works fine! Maybe needs some love on the styles when the custom thank you shows.