v3.15.0

Features

• Added an adjustMoveIndex helper for custom onMove handlers. onMove's
  index is a pre-removal slot (it counts the destination rows as displayed,
  with the dragged rows still in place), which trips up handlers that splice the
  dragged rows out before inserting them — dragging a row just below itself would
  jump it past its neighbor. adjustMoveIndex({ index, dragIds, siblingIds })
  returns the index to insert at after removal. SimpleTree/useSimpleTree are
  unaffected; they already insert before removing (issue #247). (#381)