message: Add get_index to SmallSet
  Summary: Needed for
diff: @@ -134,6 +134,12 @@ impl<T> SmallSet<T> {
  self.0.get_full(value).map(|(_, t, _)| t)
  }
  + /// Find an entry by an index.
  + #[inline]
  + pub fn get_index(&self, index: usize) -> Option<&T> {
  + self.0.get_index(index).map(|(k, _)| k)
  + }
  +
  /// Return item index, if it exists in the set
  pub fn get_index_of<Q>(&self, value: &Q) -> Option<usize>
  where
  