Roll Observatory packages and add a roll script

packages/quiver/lib/src/collection/delegates/set.dart

 // Copyright 2013 Google Inc. All Rights Reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
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   void removeAll(Iterable<Object> elements) => delegate.removeAll(elements);
 
   void removeWhere(bool test(E element)) => delegate.removeWhere(test);
 
   void retainAll(Iterable<Object> elements) => delegate.retainAll(elements);
 
   void retainWhere(bool test(E element)) => delegate.retainWhere(test);
 
   Set<E> union(Set<E> other) => delegate.union(other);
 }