aadilshabier authored May 11, 2022 and PBS committed May 11, 2022

- Remove GC dependence from UndoStackObserver 

  Removing GC from UndoStackObserver also removes it from its derived classes.

- Change CompositeUndoStackObserver::UndoObserverRecordList type to a vector

  CompositeUndoStackObserver::UndoObserverRecordList was previously an
  std::list. std::vector performs better than std::list in most cases and
  removing the GC reliance of CompositeUndoStackObserver means that we can
  safely change this into a vector.
  UndoStackObserverRecord::_observer was changed from a reference to a
  pointer to make it movable and work with vectors.