[docs] Update Strict TypeScript API guide

[huntie]

Update the docs guide for the 0.87 launch.

• Full wording pass.
• Add/consolidate ref type guidance.
• Add react-native/setup-env guidance.
• Add "Before you start", "Updating test mocks", and FAQs sections.

See react-native-community/discussions-and-proposals#1003. Replaces #5067.

[vercel]

@huntie is attempting to deploy a commit to the React Foundation Team on Vercel.

A member of the Team first needs to authorize it.

[netlify]

✅ Deploy Preview for react-native ready!

Name	Link
🔨 Latest commit	9bb4c34
🔍 Latest deploy log	https://app.netlify.com/projects/react-native/deploys/6a204dfa633cfa0009147624
😎 Deploy Preview	https://deploy-preview-5111--react-native.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify project configuration.

[cipolleschi]

Overall looks good. Left a couple of comments and one code example needs to be fixed.

[huntie]

Latest push: Address feedback, fold in opt-in → opt-out switch.

Note: Not the final version for 0.87 — will continue to refine, in a separate PR closer to the 0.87 blog post.

[huntie]

Latest: Further revised. Add "Before you start", ref types, and FAQs. Ready for launch.

Changes addressed

[Simek]

Checked out the changes on the PR preview, LGTM from the web app perspective. 👌