Improve/simplify preview builds

[mcmire]

Explanation

When we added preview builds to some polyrepos, we copied the workflow from this repo and made some improvements at the same time. This commit applies those same improvements.

• Add emoji reaction to preview build request comment when workflow begins
• Simplify preview build docs by removing external contributor-specific instructions
• Remove package scripts (the scripts used in this workflow aren't meant to be called explicitly)
• Convert script to generate reply comment to bash
• Simplify output in reply comment, and fix link to docs

References

(N/A)

Checklist

• [x] I've updated the test suite for new or updated code as appropriate
• [x] I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• [x] I've communicated my changes to consumers by updating changelogs for packages I've changed, highlighting breaking changes as necessary
• [x] I've prepared draft pull requests for clients and consumer packages to resolve any breaking changes

---

[!NOTE] Simplifies preview build publishing and docs: reacts to trigger comment, publishes via workspaces, posts concise identifiers, removes per-package preview scripts, and updates constraints.

• CI/GitHub Actions (.github/workflows/publish-preview.yml):
  • Add explicit permissions and split flow to react to the trigger comment with a 👍.
  • Use ./scripts/prepare-preview-builds.sh, publish via yarn workspaces ... npm publish --tag preview, and post identifiers via ./scripts/generate-preview-build-message.sh.
  • Standardize GH_TOKEN usage and job dependencies; avoid running on forks.
• Docs (docs/contributing.md):
  • Rename and simplify preview build instructions; remove fork-specific publishing steps.
  • Add clearer usage examples for Yarn Modern/Classic and NPM; add guidance for updating preview builds.
• Repo scripts:
  • Add scripts/generate-preview-build-message.sh; remove scripts/generate-preview-build-message.ts.
  • Remove root prepare-preview-builds and publish-previews scripts from package.json.
• Packages (packages/*/package.json):
  • Remove scripts.publish:preview across packages.
• Tooling (yarn.config.cjs):
  • Drop constraints enforcing publish:preview script; keep other constraints unchanged.

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[mcmire]

Hmm, it seems that the changelog checker workflow is incorrectly requiring changes to changelogs. It needs to omit changes to scripts. I'll make a ticket. I'm adding no-changelog in the meantime.