Slate v2 Operation Location Scrubber Surface Recovery

Goal

Recover the remaining small utility layer still claimed by the docs:

• Location.*
• Span.*
• Operation.*
• Scrubber.*

Completed

• restored Location.isLocation(...), Location.isPath(...), Location.isPoint(...), Location.isRange(...), and Location.isSpan(...)
• restored Span.isSpan(...)
• restored Operation.*:
  • isNodeOperation
  • isOperation
  • isOperationList
  • isSelectionOperation
  • isTextOperation
  • inverse
• restored Scrubber.setScrubber(...) and Scrubber.stringify(...)
• widened set_selection to carry full properties / newProperties state so Operation.inverse(...) is honest for selection operations
• widened the source barrel exports accordingly
• synced the operation and scrubber docs to the live surface

Verification

• yarn test:custom
• yarn lint:typescript