React DevTools 7.0.1 -> 8.0.0

[hoxyq]

Summary

• Bump React DevTools from 7.0.1 to 8.0.0 (packages + extension manifests only; no publish).
• scripts/devtools/prepare-release.js only supports minor/patch, so this major bump is manual.
• Changelog is curated from DevTools commits since 7.0.1 (features vs bugfixes; internal/test-only changes omitted).

Test plan

• Confirm published package versions would be 8.0.0 for react-devtools, react-devtools-core, and react-devtools-inline
• Confirm Chrome/Edge/Firefox extension manifests show 8.0.0
• Review packages/react-devtools/CHANGELOG.md 8.0.0 section for accuracy before undrafting

[github-actions]

No size report: this pull request only touches packages/react-devtools, which does not affect production bundle size.

_{Generated by sizebot against 5249653}