Slate v2 ReactEditor Root/Window Recovery

Goal

Recover the remaining cheap, honest ReactEditor root/window helpers on top of the mounted bridge.

Current Batch

1. restore getWindow
2. restore findDocumentOrShadowRoot
3. restore hasRange
4. widen runtime proof and sync docs/ledgers

Result

• restored ReactEditor.getWindow
• restored ReactEditor.findDocumentOrShadowRoot
• restored ReactEditor.hasRange
• widened runtime proof for both the mounted document seam and a mounted shadow-root seam
• updated the ReactEditor docs and RC ledgers to carry the recovered helper surface explicitly

Verification

• yarn workspace slate-react run test
• yarn test:custom
• yarn lint:typescript