Fix console errors - hydration from form & iframe

[rchlfryn]

Description

Fix a React hydration error caused by the Form block generating a random UUID on each render via generateInstanceId().
Also fixes iframe error suggestion to add allow-presentation
YouTube "Watch on YouTube" button:

• allow-popups — permits the iframe to open new windows/tabs at all
• allow-popups-to-escape-sandbox — lets those opened windows/tabs run without inheriting the sandbox restrictions

Without allow-popups, the "Watch on YouTube" link would be blocked entirely. Without allow-popups-to-escape-sandbox, it opens but the new tab is still sandboxed, causing the error.

Related Issues

Fixes #861

Issues

Form Hydration error

iframe error

Key Changes

• Replace generateInstanceId() (which called uuidv4()) with React's useId() hook, which produces stable, SSR-safe IDs
• Delete the now-unused generateInstanceId utility
• Add allow-presentation and allow-popups-to-escape-sandbox to GenericEmbed

How to test

1. Load a page with a Form block and generic embed to page
2. Confirm no hydration mismatch warnings or iframe warnings in the console
3. Confirm "Watch on YouTube" button opens new tab to youtube
4. Confirm the form and embed still renders and submits correctly

Video

https://www.loom.com/share/01a2933b7559456986295cce846a0a89

[github-actions]

Preview deployment: https://fix-form-hydration-error.preview.avy-fx.org

[github-actions]

🚀 This is included in version v1.8.0